a- (Gr. a-: without) prefix. Meaning without or lacking.
ab- prefix. Meaning away from.
ABA See abscisic acid.
abaxial (L. ab: from; axis: axle) adj. That surface of any structure which is remote or turned away from the axis, facing away from the stem of a plant, such as the lower surface of a leaf. Cf. adaxial, lateral, median.
abaxially adv. See abaxial.
abbreviate (L. abbreviare: to shorten) adj., v. Shortened. To shorten.
abbreviated (L. abbreviare: to shorten) adj. Shortened, as when one part is shorter than another. Syn. abridged.
aberrant (L. aberrare: to deviate) adj. Different from the usual; atypical; abnormal.
abiotic (Gr. a-: without; bios; life) adj. Nonliving, as opposed to biological; pertianing to or characterized by the abence of life or living organisms. Also abiotical.
abiotical See abiotic.
abiotically adv. See abiotic.
abiotic stress Nonliving environmental factors such as frost, drought, excessive heat, high winds, etc., that can have harmful effects on plants.
abiotic transformation Any process in which a chemical in the environment is altered by nonbiological mechanisms, e.g., by exposure to sunlight.
abortifacient adj., n. (A substance or device) inducing abortion.
abortion (L. abortio: abortion) n. The failure of a structure or organ to develop.
abortive (L. abortivus: born prematurely) adj. Not fully or properly developed; rudimentary; e.g., imperfectly developed spores.
above adv. Refers to the adaxial surface of a leaf, petal, sepal or scale. Refers to the part of a stem, bulb, tuber, branch, or inflorescence that is the greatest distance from the attachment, following the stem/branch; if a branch arches with a flower at the tip drooping nearly to the ground, the flower is said to be above the highest point of the branch.
abrupt (L. abruptus: broken off) adj. Terminating suddenly rather than gradually, as in leaves quickly constricted to a narrow acumen. Cf. truncate.
abruptly pinnate Pinnate without an odd leaflet at the tip. Syn. even pinnate.
abscise (L. abscidere: to cut off) v. To cut off, to separate by abscission.
abscised adj. See abscise.
abscisic acid A naturally occurring plant growth substance that appears to be involved primarily in seed maturation and in regulating closure of leaf pores (stomata). In seeds, it promotes the synthesis of storage protein and prevents premature germination. In leaves, abscisic acid is produced in large amounts when the plant lacks sufficient water, promoting closure of stomata and hence reducing further water losses. It was formerly believed to play a role in abscission, hence the name.
abscising See abscise.
abscissile adj. Of an organ that is shed. See abscission.
abscission (L. abscindere, to cut off) n. The normal shedding, separation, from the body of a plant, caused by the breakdown of thin-walled cells at the base of a structure, of an organ that is mature or aged, e.g. a ripe fruit, an old leaf. The process is controlled by growth substances, notably auxins; it involves the formation of an abscission zone, at the base of the part, within which a layer of cells (abscission layer) breaks down. Also cladoptosis.
abscission zone The area of separation when a plant sheds a leaf, flower or fruit.
absorption spectrum A graph of the amount of light a substance absorbs, plotted as a function of energy, frequency, or wavelength.
acantha (Gr. akantha: thorn) n. A thorn or spine.
acanthocarpous (Gr. akantha: thorn; karpos: fruit) adj. Having prickly or spiny fruit.
acanthocyte n. Needle-like crystalline deposit on the mycelium of certain mushrooms.
acanthoid (Gr. akantha: thorn; eidô: to seem) adj. Spiny; spinous.
acarpic (Gr. a-: without; karpos: fruit) adj. Without fruit.
acarpous (Gr. a-: without; karpos: fruit) adj. Without carpels; lacking a gynoecium.
acaulescent (Gr. a-: without; kaulos: stalk) adj. Without a stem, or the stem so short that the leaves are apparently all basai, as in the dandelion. Note: the peduncle should not be confused with the stem.
accessory adj., n. Auxiliary, subsidiary; as the parts of a flower beyond the necessary male and female organs, such as petals and sepals.
accessory bud An extra bud in a leaf axil; a bud that is situated at the side of or above an axillary bud; a bud which is at or near the nodes but not in the axils of the leaves.
accessory cell See subsidiary cell.
accessory chromosome A supernumerary, or B-, chromosome. Its uncritical use in bryophyte cytology as a synonym for m-chromosome has led to inaccuracy.
accessory flower parts Sepal and petal organs found on flowers. The sepals and petals are not essential for pollination but may aid in attracting insects or other organisms.
accessory fruit A fruit, or group of fruits derived from one flower, in which the conspicuous, fleshy portion develops from the receptacle and is shed with the true fruit(s) attached. A fleshy fruit developing from a succulent receptacle rather than the pistil. The ripened ovaries are small achenes on the surface of the receptacle, as in the strawberry.
accessory organs Parts of a flower that are not directly connected with male and female organs, e.g., petals and sepals, etc.
accessory pigment A photosynthetic pigment that traps light energy and channels it to chlorophyll a, the primary pigment, which initiates the reactions of photosynthesis. Accessory pigments include the carotenoids, phycobiliproteins, and chlorophylls b, c, and d.
acclimatable adj. See acclimate.
acclimate v. To adapt to a new environment, or a change in the environment.
acclimation n. See acclimate.
acclimatization The physiological process by which an organism adapts to a new environment. Syn. adaptation.
accrescent (L. accrescere: to carry on growing) adj. Increasing in size with age, as the calyx of some plants after flowering.
accumbent (L. accumbere: to lie, recline) adj. Lying against something; of the orientation of an embryo, with the radicle lying against the edges of the two cotyledons.
accumbent cotyledons Cotyledons lying against the radicle along one edge. Cf. incumbent cotyledons.
acephalous (Gr. a-: without; kephalê: head) adj. Headless, or with the heads much reduced.
aceriform adj. Shaped like a maple leaf.
acerose (L. acer: pointed, sharp) adj. Needle-shaped, as the leaves of pine or spruce; narrower than subulate, tapering more gradually to a point.
acetabuliform (L. acetabulum: vinegar cup: forma: shape) adj. Concave, with slightly inturned border; saucer shaped, as the fructification of certain lichens.
acetate n. A salt, ester or the conjugate base of acetic acid.
acetocarmine n. A solution of acetic acid and carmine, used as a stainer.
acetocarminic adj. Of acetocarmine
acetogenins n. Polyketides derived from acetate with 35 to 37 carbon atoms in a single almost unbranched chain, substituted by 6 to 8 oxygen atoms.
acetylcholine n. A white crystalline derivative of choline that is released at the ends of nerve fibers in the somatic and parasympathetic nervous systems and is involved in the transmission of nerve impulses in the body.
acetylenes n. The simplest of a class of triple-bonded hydrocarbons.
acetylsalicylic acid See aspirin. aceous suffix. Forming adjectives in the sense: 'of the nature of'.
acheilary See achilary.
achene (Gr. a-: without; khainen: to open) n. A dry, indehiscent fruit formed from a superior ovary of one carpel and containing one seed, attached to the fruit wall at one point only, which is free from the pericarp (often applied, less correctly, to the one-seeded fruits of Asteraceae). An example is the feathery achene of clematis, a strawberry pip. Variants of the achene include the caryopsis, cypsela, nut, and samara. (Also written akene). See also etaerio.
achenecetum n. A cluster of small seeds (achenes), as in buttercups, Ranunculus.
achenocarp (Gr. a-: without; khainô: to open; karpos: fruit) n. Any dry fruit that does not open by itself.
achenodia See achenodium.
achenodium n. (pl. achenodia) See schizocarp.
achilary adj. Having no labellum ou lip, or one that is undevelopped, as in the flower of some Orchid blossoms.
achiral adj. Said of molecules which are superposable to their mirror images. Synonym: amphichiral
achlamydeous (Gr. a-: without; khlamys: cloak) adj. Without a perianth, i.e. without calyx and corolla, as the flowers of a willow.
achlorophyllous (a-: without; Gr. chloros, light green, greenish yellow: phullon, leaf) adj. Without chlorophyll, as in plants or plant structures which are not green.
acicula (L. acicula: small needle) n. (pl. aciculae) A small needle-like or bristle-like structure. Syn. aciculum.
aciculae See acicula.
acicular (L. acicula: small needle) adj. Slender and pointed; needle-like and with a sharp point.
aciculate (L. acicula: small needle) adj. Finely scored on the surface, as if scratched by a pin; needle-shaped; having aciculae.
aciculum n. (pl. aciculums, acicula) See acicula.
acidophil See acidophile.
acidophile (L. acidus: sour, acid; philos: loved, friend) adj., n. Acid-loving. A microorganism that can, or must, live in an acidic environment (opposed to basiphile). Cf. basiphile, alkaliphile. Also acidophil, acidophilous.
acidophilic adj. See acidophile.
acidophilous See acidophile.
acid rain Rain which has turned acidic due to the presence of sulfur or nitrogen oxides in the atmosphere. Acid rain can harm and even kill plants and aquatic life.
acid soil Soil with a pH level below 7 is considered acidic; also called sour.
acidulous (L. acidulus: sourish) adj. Slightly acidic.
acies (L. acies: sharp part) n. The edge of some angled stems.
acinaceous (L. acina: small berry, grape) adj. Covered or filled with kernels; having many small seeds, as a grape.
acinacifoliate See acinacifolious.
acinacifolious (L. acinaces: scimitar; folia: leaf) adj. Having scimitar-shaped leaves. Also acinacifoliate.
acinaciform (L. acinaces: scimitar; forma: shape) adj. Scimitar-shaped, sickle-shaped.
acinarious (L. acina: small berry, grape) adj. Covered with globose vesicles resembling grape seeds, as certain algae.
acini See acinus.
aciniform (L. acinus: small berry, grape; forma: shape) adj. Clustered like grapes; acinous.
acinose (L. acina: small berry, grape) adj. Resembling a bunch of grapes; consisting of acini. Also acinous.
acinous See acinose.
acinus (L. acinus: small berry, grape) n. (pl. acini) One of the small drupelets or berries of an aggregate, baccate fruit, as the blackberry; a berry, as a grape, currant, etc.
acorn n. The hard-shelled, one-seeded, indehiscent fruit of the oaks (Quercus) which consists of a single, large seed, a nut which is partly enclosed at the base by the hard woody cupule, or cap, of indurated bracts.
acotyledonous (Gr. a-: without; kotyloeidês; cup like) adj. Without cotyledons
acquired character Modification impressed on an organism by environmental influences during development.
acrandrous adj. With antheridia produced at apex of stem.
acre n. A land measurement of 43 560 square feet (about 210 feet by 210 feet), roughly the size of a football field.
acrid (L. acer, acris: pointed, sharp) adj. A sharp, bitter, or biting taste.
acrocarpous (Gr. akros: highest, top; karpos: fruit) adj. Of mosses, having the sporophyte terminal on a stem or ordinary branch; having the fruit at the end of the primary axis; with gametophyte producing sporophyte at apex of a stem or main branch. Acrocarpous mosses generally grow erect in tufts (rather than mats) and are sparsely or not branched. Cf. pleurocarpous.
acrocidal capsule A dry fruit which dehisces by slits at the terminal.
acrodendrophilous (Gr. akros: highest, top; dendron: tree; philos: friend) adj. Thriving in tree tops.
acrodrome (Gr. akros: highest, top; dromos: race) adj. Running to a point; of a leaf with the main veins ending at the leaf tip. Also acrodromous.
acrodromous (Gr. akros: highest, top; dromos: race) adj. Of leaves with two or more primary or strongly developed secondary veins running in convergent arches towards the apex, with the arches not recurved at base. Cf. brochidodromous, eucamptodromous, semicraspedodromous.
acrogen (Gr. akros: highest, top; genea: what is generated) n. A non-flowering plant which grows and produces its reproductive structures only at the apex, as ferns and mosses.
acrogenic See acrogenous.
acrogenous (Gr. akros: highest, top; genea: what is generated) adj. Growing from the apex. See acrogen.
acrogynous (Gr. akros: highest, top; gynê: woman, female) adj. Having the archegonia arising from the apical cell of the stem, thereby terminating its growth, as certain liverworts. Cf. anacrogynous.
acropetal (Gr. akros: highest, top; L. petere, to seek) adj. Near the tip rather than the base. Arising or developing in a longitudinal sequence beginning at the base and proceeding towards the apex; i.e. developing from below upwards, as the flowers in an indeterminate inflorescence. Cf. basipetal.
acrophilous (Gr. akros: highest, top; philos: friend) adj. Thriving in alpine regions.
acroscopic (Gr. akros: highest, top; Gr. skopeô: to watch) adj. Facing the tip or apex; applied to the triangular surface of a merophyte in direct contact with the apical cell. Cf. basiscopic.
acrostichoid (Gr. akros: highest, top; Gr. stikhos: row; eidô: to look like) adj. Of sporangia, densely covering the abaxial surface of the fertile frond, i.e. not in distinct groups; of ferns, having the sporangia arranged as above.
acrotonic (Gr. akros: highest, top; tonos: intensity, strength) adj. Of flowering seasonal shoots which produce leaves below the inflorescence; of growth that is intensified in the upper part of a plant, resulting in a more or less canopic shaped plant. Cf. basotonic, mesotonic.
acteoside See verbascoside.
actinocytic adj. Said of stomata, with five or more somewhat radially enlarged or elongated subsidiary cells surrounding the guard cells. Cf. anisocytic, anomocytic, cyclocytic, diacytic, paracytic, staurocytic, tetracytic.
actinodromous adj. Said of palmate leaf venation, with three or more primary veins arising from at or near the base, ascending or diverging, whether or not reaching the margin, cf. acrodromous.
actinomorphic (Gr. aktis: ray; morphe: form) adj. Descriptive of a flower or set of flower parts which can be cut through the center into equal and similar parts along two or more planes; having radial symmetry. Cf. zygomorphic.
actinomorphous See actinomorphic.
Actinomycetales (Gr. actis: ray; mukê: mushroom) n. An order of bacteria consisting of moldlike, rod-shaped, clubbed or filamentous forms that tend to form branching filaments.
actinomycete (Gr. actis: ray; mukê: mushroom) n. Any of various filamentous or rod-shaped, often pathogenic microorganisms of the order Actinomycetales that are found in soil and resemble bacteria and fungi.
actinostele (Gr. aktis: ray; stêlê: stele, standing block) n. A stem in which xylem occupies the center but the phloem occupies indentations in the xylem. This makes the xylem resemble a star; e.g. the stem of Psilotum. See also stele.
actinostelic (Gr. aktis: ray; stêlê: stele, standing block) adj. Said of a vascular strand where ribs radiate outward.
active transport The movement of a chemical substance by the expenditure of energy through a gradient (as across a cell membrane) in concentration or electrical potential and opposite to the direction of normal diffusion.
aculeate (L. aculeus: small needle) adj., n. Prickly; pointed, incisive; covered with prickles. A hymenopterous insect of the section Aculeata, which includes bees, wasps, and ants; stinging. Also aculeated, aculeiform.
aculeated See aculeate.
aculei See aculeus.
aculeiform (L. aculeus: small needle; forma: shape) adj. Shaped like a prickle. Also aculeate.
aculeolate (L. aculeus: small needle) adj. Minutely aculeate, minutely prickly; covered with tiny prickles. See aculeate.
aculeus (L. aculeus: small needle) n. (pl. aculei) A prickle growing from bark.
acumen (L. acumen, a point, a sting) n. (pl. acumina) The point of an acuminate leaf; apex; a slender, tapering point.
acumina See acumen.
acuminate (L. acumen, a point, a sting) adj. Drawn out into a long point; tapering gradually to a protracted point; slenderly tapered with an angle of less than 45º; longer than acute. The shape of a tip or base of a leaf or perianth segment where the part tapers gradually and often in a concave manner.
acumination See acuminate.
acuminose (L. acumen, a point, a sting) adj. Rather less gradual than acuminate.
acutangular (L. acutus: acute, pointed, sharp; angulus: angle, corner) adj. Refers to a stem that is sharply angled, acute-angled.
acute (L. acutus: acute, pointed, sharp) adj. Sharp at the end; ending in a sharp point; terminating in a distinct but not protracted point, the converging edges separated by an angle less than 90 degrees but greater than 45 degrees; tapering without curvature to a point.
acyclic (Gr. a-: without; kyklikos: circular) adj. With the floral parts arranged spirally rather than in whorls.
acylation n. The stabilization by the introduction of an acid radical from acids such as coumaric, ferulic, or caffeic acids into e.g. acylated anthocyanins.
ad- prefix. Meaning to or toward.
adaptability (L. adaptare: to fit, to adjust) n. Proficiency of an organism to make changes improving survivability and reproduction in its habitat.
adaptation (L. adaptare: to fit, to adjust) n. Change in a organism resulting from natural selection; a structure which is the result of such selection. The process by which individuals (or parts of individuals), populations, or species change in form or function in such a way to better survive under given environmental conditions.
adaptedness (L. adaptare: to fit, to adjust) n. The genetic characteristics by which an organism is suited to its environment.
adaptive capacity The genetically set range or flexibility of reactions of an organism enabling it to respond in different ways to differing conditions.
adaptive radiation The evolution of new species or subspecies to fill unoccupied ecological niches. The evolution and diversification of many species from a single ancestor (e.g., the adaptive radiation of the finches of the Galapagos Islands).
adaptive selection The evolution of comparable forms in separate but ecologically similar areas.
adaxial (L. ad: toward; axis: axle) adj. Facing toward the stem of a plant; pertaining to the side of an organ toward the axis, especialy of the upper, ventral side of a leaf or costa. Cf. abaxial.
adaxially adv. See adaxial.
addition polymer A polymer made by the addition of monomers together, the mechanism for which makes it a chain polymer. The most important examples are the polyalkenes, the archetypal example of which is polyethylene. Cf. condensation polymer.
additive genetic variance That genetic variation (variance) which is due to additive effects of genes.
adenophore (Gr. adên: gland; phora: carrying) n. The stalk of a nectary.
adenophorous (Gr. adên: gland; phora: carrying) adj. Gland-bearing.
adenophyllous (Gr. adên: gland; phyllon: leaf) adj. Having gland-bearing leaves.
adenosine diphosphate An ester of adenosine that is reversibly converted to ATP for the storing of energy by the addition of a high-energy phosphate group, abbreviated ADP.
adenosine triphosphate A phosphorylated nucleoside that supplies energy for many biochemical cellular processes by undergoing enzymatic hydrolysis especially to ADP. An energy-rich phosphorous compound that is important in the transfer of energy in organisms, abbreviated ATP.
adherent (L. adhærere: to stick, to cling) adj. Sticking together, but not fusion, of unlike parts, as the anthers to the style, the bracts and perianth of leafy liverworts. The attachment is not as firm or solid as adnate. Cf. coherent, adnate.
adiaspore n. A spherical spore with a rigid cell wall (chlamydospore) produced in the lungs by the enlargement of an inhaled conidium of Emmonsia.
adjacent (L. adjacere: to lie by, to be situated by) adj. Next to each other, but without touching or overlapping.
adjuvant n. A pharmacological agent added to a drug to increase or aid its effect. An immunological agent that increases the antigenic response. A coadjuvant
admedial adj. Towards the midline of the lamina. Cf. exmedial
adnate (L. adnatus, var. of agnatus, past participle of agnascor: grow on, beside) adj. Fused to an organ of a different, unlike parts, e.g. perianth and bract, a calyx adnate to the ovary. Cf. connate.
adnexed adj. Said of mushrooms with the gills narrowly attached to the stalk, i.e. the gills are lightly adnate.
ADP See adenosine diphosphate.
adpressed adj. Lying close to another organ, but not fused to it.
adscendent See ascending.
adsurgent See ascending.
adunc (L. ad: towards; uncus: hook) adj. Curved inward; hooked.
aduncate adj. Hooked. See adunc.
advanced generations synthetic varieties Advanced generations derived from an initial intercrossing of a specific set of clones or seed-propagated lines; usually stable for only limited number of generations. Examples: `Ranger' and Moapa alfalfa, `Saratoga' bromegrass, `Pennlate' orchardgrass .
advance growth Seedlings and saplings appearing under the canopy ready to fill in forest openings made available by the death of a mature tree from logging, lightning kills, etc. Syn. young growth.
adventitious (L. adventicius: fortuitous, coming from outside, unexpectedly) adj. Plant structures or tissue occurring sporadically in an abnormal position, i.e. in a position other than the usual location, i.e. coming from another source, i.e. not inherent or innate, e.g. roots arising from the shoot system, from stems or leaves, buds arising elsewhere than in axils of leaves, rhizoids arising from leaf or costal cells.
adventitious root A root that arises from a stem for example, rather than from the primary root.
adventitious embryony The production of an embryo/seed directly from somatic tissue of the ovule without fertilisation. Cf. agamospermy, apogamy, apomixis, apospory, vegetative reproduction.
adventitious species An alien or exotic species; an invasive species.
adventitiously adv. See adventitious.
adventive (L. advenire: to arrive, to come to) adj. A plant that is not native to the environment, a plant introduced recently, in particular since colonisation by man, e.g. adventive species, or, in reference to a structure that arises from a dedifferentiated cell, such as an adventive branch. Cf. introduced.
adventive taxa Organisms that were not native to an area, and have now naturalized.
adverse (L. adversus: vis-à-vis, in front) adj. Turned towards the axis, as a leaf. Opposed to averse.
aecia See aecium.
aecidia See aecidium.
aecidium (Gr. aikia: injury, assault) n. (pl. aecidia) An aecium in which the spores are always formed in chains and enclosed in a club shaped peridium. Vegetative fruiting body of the Uredinales at the end of the haploid stage containing dikaryotic aeciospores.
aeciospore (Gr. aikia: injury, assault; spora: seed) n. A spore borne by an aecium.
aecium (Gr. aikia: injury, assault) n. (pl. aecia) The sorus of rust fungi which arises from the haploid mycelium, commonly accompanied by spermogonia and bearing chainlike or stalked spore.
aeolian (L. Æolus: Aeolus [god of the winds]) adj. Refers to the wind, or to soil which has been moved by wind; of or caused by the wind; wind-blown. Syn. eolian.
aeon (Gr. aiôn: long space of time) n. An indefinitely long period of time; age; the largest division of geologic time, comprising two or more eras. See also eon.
aequilateral (L. aequus: equal) adj. Equal-sided, as opposed to oblique (in leaves).
aerating root A root structure that rises above ground, usually above water, to allow the plant to absorb air.
aerenchyma (Gr. aêr: air; en: in; khymos: sap, juice) n. Parenchyma tissue (spongy tissue) with large and abundant intercellular air spaces, found especially in many aquatic plants; air-storing tissue; resembles the tissue of cork.
aerial (Gr. aêr: air) adj. Occurring above ground or water, as the adventitious roots of some trees.
aerial roots Roots borne wholly above ground, as the attachments of vine forms of Toxicodendron radicans which penetrate tree bark. Rooting shoots of epiphytes.
aeriferous (L. aer, aeris : air, ferre : to carry) adj. Containing or conveying air.
aerobe n. See aerobic.
aerobic (Gr. aêr: air; bios: life) adj. Of an organism or tissue living, active, or occurring only in the presence of oxygen; pertaining or caused by the presence of oxygen.
aerobically adv. See aerobic.
aerobiosis (Gr. aêr: air; bios: life) n. All life that grows in the presence of free oxygen.
aerophyte (aêr, aeros: air; phyton: plant) n. A plant that derives moisture and nutrients from the air and rain; it usually grows on antoher plant but is not parasitic on it. A plant growing on aerial parts of another plant. Cf. epiphyte.
aeroplankton (aêr, aeros: air; plagktos: wandering) n. Microorganisms which float in the air, as plankton floats in water.
aerotaxis n. An involuntary response of a living thing to a gas, such as a plant curving toward a more concentrated source of carbon dioxide.
aerotropic (Gr. aêr, aeros: air; tropos: direction) adj. Taking a particular direction under the influence of air.
aerotropism (Gr. aêr, aeros: air; tropos: direction) n. Aerotropic tendency of growth.
aeruginose adj. Bluish green in color.
aestival (L. æstivalis: of the summer) adj. Pertaining or appropriate to the summer; flowering or appearing in the summer. Syn. estival.
aestivate v. To become dormant in summer.
aestivation (L. æstivus: of the summer) n. The arrangement of sepals and petals or their lobes in an unexpanded flower bud, before it opens. Cf. vernation.
affinity (L. affinitas: connection by marriage) n. The phylogenetic relationship between two organisms or group of organisms resulting in a resemblance in general plan or structure, or in the essential structural parts. That relationship between organisms which shows they share a common origin; used occasionally to show the similarity among communities.
affixed (L. affixus, adfixus: past participle of adfingere: to tie) adj. Of aquatic plants, rooted in soil but growing in open water.
afforestation n. The process of starting a new forest in an area where none existed; to do the same to replace a previous growth is reforestation. Also afforestment.
afforestment See afforestation.
afoliate (Gr. a-: without; L. folium: leaf) adj. Without leaves.
aftermath n. A second growth crop, also called a rowen. The outcome, especially of a disaster, as in the aftermath of a forest fire.
after-ripening n. Metabolic changes that must take place in a seed to overcome dormancy. The dormancy period following seed formation, necessary for embryo changes that insure germination; a period during which certain changes must occur in some dormant but fully developed seeds before germination.
agameon (Gr. a-: without; gamos: marriage) n. An organism that reproduces asexually only, without producing gametes, sperm or eggs; a species that contains only apomictic individuals. A species that contains only apomictic individuals. Cf. agamospecies.
agamete (Gr. a-: without; gametês, gametis: spouse) n. An asexual reproductive cell, as a spore, which forms a new organism, without fusion with another cell.
agamic (Gr. a-: without; gamos: marriage) adj. Asexual; occuring without sexual union; germinating without impregnation; not gamic; cryptogamic. Also agamous.
agamogenesis (Gr. a-: without; gamos, marriage; genesis: origin) Asexual reproduction by buds, offshots, cell division, etc.
agamospecies (Gr. a-: without; gametês, gametis: spouse; species: species, type) n. A group of individuals in which reproduction is almost exclusively by asexual means; species that do not require fertilisation of male and female gametes to produce offspring. Also agameon. Cf. agamogenesis.
agamospermy (Gr. a-: without; gamos, marriage; sperma: seed) n. Asexual reproduction. See apomixis.
agamosporous (Gr. a-: without; gamos, marriage; spora: seed) adj. Of ferns having a life cycle in which chromosome segregation and recombination does not take place.
agamous (Gr. a-: without; gamos, marriage) adj. Without stamens or pistils; neuter, sterile. Also agamic.
agar n. A gelatinous substance produced by red algae, often used as a culture medium. Also agar-agar.
agar-agar See agar.
agaric (Gr. agarikon: agaric, a kind of mushroom) n. A fungus belonging to a large worldwide order (Agaricales). The group includes many edible mushrooms, such as the white mushroom (Agaricus bisporus) and field mushroom (A. campestris), as well as the poisonous death cap (see Amanita). The visible part of the fungus consists of a stipe (stalk) bearing a cap with gills on the undersurface. Phylum: Basidiomycota.
agaricaceous (Gr. agarikon: agaric, a kind of mushroom) adj. Belonging to the Agaricaceae, a family of fungi includin mushrooms having blade-shaped gills on the underside of the cap.
Agaricales (Gr. agarikon: agaric, a kind of mushroom) n. An order of the phylum Basidiomycota.
agaricoid (Gr. agarikon: agaric, a kind of mushroom; eidô: to look like) adj. Like an agaric.
agaricologist (Gr. agarikon: agaric, a kind of mushroom; logos: word) n. A person whous studies gilled musrooms (agarics).
Agaricus (Gr. agarikon: agaric, a kind of mushroom) n. A genus of the phylum Basidiomycota.
age unit 'stage'. Ages are subdivisions of epochs and may themselves be subdivided into chrons. An age takes its name from the corresponding stage, so like the stage name it carries the suffix '-ian' (or sometimes '-an'); the term 'age' is capitalized when used in this formal sense, e.g. 'Oxfordian Age'. An informal term to denote a time span marked by some specific feature, e.g. 'Villefranchian mammalian age'.
age and area The hypothesis (Willis, 1922) that the larger the area covered by a species, the older that species is; i.e. species are rare because they have recently evolved and haven't had time to expand their range.
age class Refers to a stand in which all the trees or other perennials started growth in the same regeneration period. A grouping of living things based on their age; for example, trees are often grouped into 10-year age classes.
ageotropic (Gr. a-: without; ge: earth; tropos: direction) adj. Said of parts that would be expected to grow as gravity pulls, but instead grow upward, such as the knee roots of cypress, Taxodium spp. Also apogeotropic.
ageotropically (Gr. a-: without; ge: earth; tropos: direction) adv. From ageotropic.
ageotropism (Gr. a-: without; ge: earth; tropos: direction) n. An upward growth, against the pull of gravity. The absence of orientation movements in response to gravity.
agglomerate adj. Together in a head, as the florets of red clover, Trifolium pratense; clustered; crowded in a dense cluster, but not cohering. Also agglomerated. Also agglomerated.
agglomerated adj. Crowded in a dense cluster, but not cohering. Also agglomerate.
agglutinated adj. Stuck together as with glue, as in pollen masses of orchids.
aggradation n. The gradual filling of depressions in the earth's surface by soil deposition, such as the deposition at a lake's bottom; or the opposite, the wearing away of mountain tops, reaching toward a level surface. The accumulation of sediment. Also used to refer to certain landforms that are growing. For example, ocean shorelines can aggrade when the soil is protected from ocean waves.
aggregate n., adj., & v. Said of fruits formed from several carpels, from separate ovaries, derived from the same flower: an aggregate fruit, as the raspberry; said of a flower formed by a cluster of florets, in a dense mass or head, but not cohering, as in composite plants: an aggregate flower. Said of a group of species comprising several very similar species that were formerly regarded as a single species. In mosses, applied to two or more sporophytes from one perichaetium. Also aggregated. See aggregate fruit.
aggregated See aggregate.
aggregate flowers Flowers crowded into dense clusters or tufts, as in Scabiosa atropurpurea.
aggregate fruit Usually applied to a cluster or group of small fleshy fruits originating from a number of separate pistils in a single flower, i.e. a fused cluster of several fruits, each one formed from an individual ovary, as in the clustered drupelets of the raspberry. See also: syncarp.
aggregate species A group of species that are so closely related that they are regarded as a single species.
aggregation n. The coming together of organisms into a group, such as seedlings growing near the base of a parent tree; a group of organisms of the same or different species living closely together but less integrated than a society. Cf. community.
aging adj. When said of a lake, refers to the enrichment of waters, rapid growth of aquatic plants, and sedimentation which accelerate the death of a lake.
aglucone See aglycone.
aglycone n. The non-carbohydrate group of a glycoside which appears on its hydrolysis. Also aglucone.
agrestal (L. ager, agri: field) adj. Growing wild; said especially of weed plants growing on farms.
agrestic (L. ager, agri: field) adj. Rural; rustic.
agrophilous adj. Refers to organisms which grow best in cultivated fields or other manmade areas.
agrostology (Gr. argrôstis: Bermudagrass [Cynodon dactylon]) n. The branch of botany dealing with grasses.
agrosystem n. Unit of land exploited by human beings for the production of plant or animal material.
agynic (Gr. a-: without; gynê: female) adj. Lacking a gynoecium; free from the pistil.
A horizon The uppermost layers of soils consisting of partly decomposed plant remains and relatively fresh leaves and other plant debris; the surface mineral layer, high in organic matter and dark in color; and the lighter colored layer where leaching of solutes and suspended materials occurs.
aianthous (Gr. ai: always; anthos: flower) adj. Flowering constantly.
air chamber A specialized internal air-containing cavity common in most complex thalloid liverworts; e.g. Marchantiales.
air pore Minute opening in the upper epidermis of most complex thalloid liverworts, functioning in gas exchange and water regulation; bordered by one or more rings of modified epidermal cells. Syn. pneumathodes. Cf. breathing pore, compound pore, simple pore, stoma.
akene n. See achene.
akinete (Gr. a-: without; kinêtis: which moves, throws) n. In certain algae, a non motile, asexual spore formed within a cell, the wall of which is fused to that of the parent cell.
ala (L. ala: wing) n. (pl. alae) A winglike extension or process; one of the two lateral petals of a papilionaceous corolla, wing or keel.
alar (L. ala: wing) adj. Pertaining to or having wings; winglike; wing-shaped; axillary.
alar cells Describing the cells at the basal angles of a leaf, commonly different from the cells of the main part of the leaf, being shorter and often nearly square, or inflated and hyaline, and often highly colored; e.g. Dicranum.
alate (L. alatus: winged) adj. Winged.
alated See alate.
albescense (L. albescere: to become white) n. The act of turning white, whitish.
albescent adj. See albescense.
albidus (L. albidus: white) Epithet of a species, meaning white, e.g. Lactarius albidus.
albino (L. albidus: white) n. adj. A flower that lacks normal color; white.
albumen (L. albumen: the white of an egg) Starchy and other nutritive material in a seed, stored as endosperm inside the embryo sac, or as perisperm in the surrounding nucellar cells; any deposit of nutritive material accompanying the embryo. A rare name for endosperm. See endosperm.
albuminous adj. With albumen.
albuminous cell A gymnosperm phloem parenchyma cell closely associated with an adjacent sieve cell; sieve cells have albuminous cells which feed them.
alburnum (L. albus, white) n. The outer, newer, usually somewhat lighter, wood of a woody stem; consists of living xylem cells, which both conduct water and provide structural support. Cf. heartwood. Syn. sapwood.
aleurone n. The outermost layer(s) of the endosperm, living cells containing proteins, the other cells being more or less dead and with much thickened walls, the lumen being more or less occluded e.g. by galactomannans (a hemicellulose).
alga (L. alga: alga) n. (pl. algae) A general name for the single-celled plant plankton, seaweeds, and their freshwater allies.
algae See alga.
algae bloom Rapid growth and death of aquatic plants, especially during hot weather in highly nutritious water; algae blooms are part of the natural annual cycle of the oceans and coastal regions. Occasionally the blooms are toxic or harmful to fish and other marine life.
algal layer A thin layer of green or blue-green algae lying just beneath the cortex of a lichen.
algin n. Alginic acid or one of its esters or salts, especially the gelatinous solution obtained as a by-product in the extraction of iodine from seaweed, (brown algae) used in mucilages, in harmaceutical preparations, and for thickening jellies
alginate n. Component of the cell walls of many rhodophytes and kelps. Alginates have an affinity for water, and so help to slow dessication when the algae are exposed to the air; they are commercially important in the production of paper, toothpaste, beer, and frozen foods. A salt or ester of alginic acid.
algoid (L. alga: alga; Gr. eidô: to look like) adj. Resembling or relating to algae.
algology (L. alga: alga; Gr. logos: word) n. The study of algae.
alien adj., n. An exotic plant; an introduced plant which has naturalized.
aliferous (L. ala: wing; ferre: to carry) adj. With wings.
aliform (L. ala: wing; forma: shape) adj. wing-shaped, winglike; alar.
aliphatic adj. Of, relating to, or designating a group of organic chemical compounds in which the carbon atoms are linked in open chains.
alkali n. A soluble salt obtained from the ashes of plants and consisting largely of potassium or sodium carbonate, e.g., a hydroxide or carbonate of an alkali metal, having marked basic properties. Alkali metal. A soluble salt or a mixture of soluble salts present in some soils of arid regions in a quantity that is detrimental to agriculture.
alkaline adj. Of, relating to, containing, or having the properties of an alkali or alkali metal; having a pH of more than 7, i.e. of a material that is basic rather than acidic.
alkaline reserve See alkali reserve.
alkaline soil Soil with a pH level above 7; basic soil; also called sweet.
alkalinity n. See alkaline.
alkaliphile n. adj. An organism that prefers, or can tolerate, alkaline conditions, typically in the range of pH 8 to 11; a type of extremophile. Cf. acidophile. Syn. basophile. Also alkalophile, alkaliphilic.
alkaliphilic See alkaliphile.
alkali reserve The total amount of dissolved substances predisposed to maintain the normal alkalinity of a body of water or an organism's internal body fluids. The amount of conjugate base components of the blood buffers; since bicarbonate is the most important of these conjugate bases, the blood bicarbonate is often considered to be equivalent. Also alkaline reserve.
alkali sink A land basin in which water evaporation produces high salt concentrations that may, or may not, support salt marsh vegetation.
alkaloid One of a group of nitrogenous organic compounds derived from plants and having diverse pharmacological properties. Alkaloids include morphine, cocaine, atropine, quinine, and caffeine, most of which are used in medicine as analgesics or anaesthetics. Some alkaloids are poisonous, e.g. strychnine and coniine, and colchicine inhibits cell division.
alkaloids See alkaloid.
alkalophile See alkaliphile.
alkanes n. Simple hydrocarbons, CH3 (CH2)n CH3, where n = 25 to 35.
alkannin n. A naphthoquinone derived from the p-hydroxybenzoic acid pathway, the coloring ingredient of alkanet; alkannin paper is an indicator of acidity, alkalis turning the paper blue, acids red (see the color changes as flowers of some Boraginaceae-Boraginoideae age).
allagostemonous (Gr. allagê: change; stêmôn: thread) adj. A flower having stamens attached to both the petal and receptacle.
allantoid (Gr. allas, allantos: sausage; eidô: to look like) adj. Sausage-shaped.
allee effect Reduction in the mean individual reproductive success in low density groups, observed in a number of sexual species.
allel See allele.
allele (Gr. allêlôn: of one another) n. One of the alternative forms of a gene. Any of the variant forms of a gene, concerned with the same characteristic, that may occur at a given gene locus. In a diploid cell there are usually two alleles of any one gene (one from each parent), which occupy the same relative position (locus) on homologous chromosomes. One allele is often dominant to the other (known as the recessive), i.e. it determines which aspects of a particular characteristic the organism will display. Within a population there may be numerous alleles of a gene; each has a unique nucleotide sequence. Also allel.
allelic adj. See allele.
allelochemicals (Gr. allêlôn: of one another; khymeia: mixture) n. Compounds that have an allelopathic effect. See allelopathy.
allelopathic adj. See allelopathy.
allelopathy (Gr. allelon: one another; pathos: what one feels) n. The influence or effect of one living plant upon another; refers to biochemical interaction between all types of plants and its effect depends on a chemical compound being added to the environment. The release of chemicals by a plant to inhibit the growth of other plants in its immediate vicinity.
allergen (Gr. allos: other; ergon: action) n. A substance which induces allergic symptoms like rash, inflammation, etc.
allergenic adj. Capable of causing allergy. See allergen.
allergy (Gr. allos: other; ergon: action) n. Sensitivity resulting in reactions such as rash, inflammation, etc., when exposed to an allergen, e.g., pollen, strawberries, etc.
alliaceous (L. alium: garlic) adj. Having the smell or taste of garlic.
alliance n. A group of plant associations classed together on the basis of similarities in floristic and sociological characters.
allitol n. A carbohydrate product resulting from the reduction of the aldehyde functional group in D-allose.
allo- (Gr. allos: other) prefix. Meaning other.
allochor (Gr. allos: other; khôreô: to move) adj. See allochory
allochory (Gr. allos: other; khôreô: to move) n. The dispersal of seed by external factors, such as wind, water, animals, etc.; this mode of dispersal is then called allochor.
allochthon See allochthonous.
allochthonous (Gr. allos: other; khthon: earth, country) adj. Originating from outside a system, such as the leaves of terrestrial plants that fall into a stream. Pertaining to materials, particularly rock masses, that formed somewhere other than their present location, and were transported by fault movements, large-scale gravity sliding, or similar processes. Autochthonous material, in contrast, formed in its present location. Landslides can result in large masses of allochthonous rock, which typically can be distinguished from autochthonous rocks on the basis of their difference in composition. Faults and folds can also separate allochthons from autochthons. Cf. autochthonous. Also allochthon.
allochtonous See allochthonous.
allogamous (Gr. allos: other; gamos: marriage) adj. Reproducing by cross-fertilization.
allogamy (Gr. allos: other; gamos: marriage) n. Cross-pollination, Cross-fertilization in plants. Opposed to autogamy.
allogenic succession The replacement of one kind of community with another because of a change in the environment which was not produced by the plants themselves, e.g., a decrease in soil moisture. Allogenic succession relates to events where the pattern of succession is determined by colonizers outside of the system. One characteristic example of allogenic succession is what happens in cow dung. There are certain species of plants and animals that inhabit this material. After the material is released from the cow, it falls to the ground where some of the seeds int he material germinate and begin to grow. This produces an 'island' of different species from what is happening around the dung.
allohexaploid adj. n. Having sex genomes with one or more sets derived from a species different from the other sets; e.g. Triticumaestivum is an allohexaploid.
allopathic adj. Of or pertaining to allopathy
allopathically adv. See allopathy.
allopatric (Gr. allos: other; patra: fatherland) adj. Of two or more species, having different, separate ranges of distribution, occupying different geographie regions. Cf. sympatric.
allopathy n. A method of treating disease with remedies that produce effects different from those caused by the disease itself.
alloploid (Gr. allos: other; eidos: form) adj., n. An individual which arise after natural or experimental crossing of 2 or more closely-related species or genera and contain the chromosome sets of the parents.
alloploidy (Gr. allos: other; eidos: form) n. Polyploid condition in which the contributing genomes are dissimilar. When the genomes are doubled fertility is restored and the organims is an amphidiploid.
alloploidion n. A species derived from allopolyploidy; individuals are usually highly variable and apomixis is not present.
allopolyploid (Gr. allos: other; polys: many; eidos: form) adj., n. A polyploid individual or strain having a chromosome set composed of two or more chromosome sets derived more or less complete from different species. A polyploid organism, usually a plant, that contains multiple sets of chromosomes derived from different species. Hybrids are usually sterile, because they do not have sets of homologous chromosomes and therefore pairing cannot take place. However, if doubling of the chromosome number occurs in a hybrid derived from two diploid (2n) species, the resulting tetraploid (4n) is a fertile plant. This type of tetraploid is known as an allotetraploid; as it contains two sets of homologous chromosomes, pairing and crossing over are now possible. Allopolyploids are of great importance to plant breeders as advantages possessed by different species can be combined. The species of wheat, Triticum aestivum, used to make bread is an allohexaploid (6n), possessing 42 chromosomes, which is six times the original haploid number (n) of 7. See also amphidiploid. Cf. autopolyploid.
allopolyploidy See allopolyploid.
allotetraploid (Gr. allos: other; tetras: four; eidos: form) adj. Having four genomes with two sets (rarely one) coming from a different species than the others. an interspecific hybrid having a complete diploid chromosome set from each parent form. (syn. amphidiploid)
allotrophic adj. Refers to lakes or ponds which receive organic materials from the surrounding land by washing. Lakes in which most of the organic matter is from autochthonous sources are referred to as 'autotrophic', whereas those dominated by the input of paralimnetic particulate organic matter (POM) and dissolved organic matter (DOM) are termed 'allotrophic'.
allotropous (Gr. allos: other; tropos: way) adj. Of flowers having the nectar accessible to any species of insect.
allotropous flower A flower shaped so that its nectar is readily available to pollinators.
allotype (Gr. allos: other; typos: image) n. A type specimen of the opposite sex to that of the holotype.
alluvia See alluvium.
alluvial (L. alluvio: alluvion) adj. Of or pertaining to alluvium (i.e. organic materials deposited by running water).
alluvial fan A delta at the mouth of a stream or river formed by the depositing of transported materials when the flow lessens. The land counterpart of a delta: an assemblage of sediments marking place where a stream moves from a steep gradient to a flatter gradient and suddenly loses transporting power. Typical of arid and semiarid climates but not confined to them.
alluvial soil Soil deposits at the mouth of a stream or river, characterized by little or no modification of the original transported material by soil-forming processes. Alluvial soil is formed when a soilcarrying stream gradually loses its carrying capacity with decreasing velocity. In slowing down, a river does not have sufficient power to keep the large particles of soil suspended; these particles settle to the riverbed. Further decrease in velocity causes smaller particles to settle. As the river becomes slow and sluggish (as in the lowlands where its gradient becomes small), it holds only the extremely fine particles in suspension. These particles are deposited, finally, at the mouth of the river, where they form deltas of fine-grained soil.
alluvion See alluvium.
alluvium (L. alluvio: alluvion) n. (pl. alluviums, alluvia) A mineral rich deposit of sand, mud, etc., formed by flowing water; e.g. the oils of flood plain. Syn. alluvion.
allyl n. The univalent, unsaturated organic radical C3H5.
allylic adj. See allyl.
alm n. A high mountain meadow, either alpine or subalpine.
almond n. A deciduous tree (Prunus dulcis), native to Asia and northern Africa and having alternate, simple leaves, pink flowers, and leathery fruits. The ellipsoidal kernel of this tree, either eaten as a nut or used for extraction of an oil for flavoring. Any of several other plants, such as the Indian almond, especially those with fruits or seeds suggestive of the almond. Something having the oval form of an almond.
alpage n. An upland pasture consisting of natural plants which are used for grazing animals at the height of summer.
alpestrine adj. Pertaining to high mountains, to regions above timberline.
alpine adj. Of or pertaining to areas above timber line; growing above timberline.
alterative (L. alteratio: change) adj., n. Tending to alter or produce alteration. Tending to restore to normal health. Herbal medicines which can work a gradual change in the system. A treatment or medication that restores health.
alternate (L. alternatus: done one after another) adj. Said of leaves occurring one at a node; said also of members of adjacent whorls in the flower when any member of one whorl is in front of or behind the junction of two adjacent members of the succeeding whorl; said of leaves or other lateral organs, borne singly at different heights on the axis; of floral parts, on a different radius, e.g. describing the position of stamens with respect to petals. Cf. opposite.
alternate host A second host species without which a parasite cannot complete its life history.
alternately adv. See alternate.
alternation of generations The occurrence within the life cycle of an organism of two or more distinct forms (generations), which differ from each other in appearance, habit, and method of reproduction. The phenomenon occurs in some protoctists, certain lower animals (e.g. cnidarians and parasitic flatworms), and in plants. The malaria parasite (Plasmodium), for example, has a complex life cycle involving the alternation of sexually and asexually reproducing generations. In plants the generation with sexual reproduction is called the gametophyte and the asexual generation is the sporophyte, either of which may dominate the life cycle, and there is also alternation of the haploid and diploid states. Thus in ferns the dominant plant is the diploid sporophyte; it produces spores that germinate into small haploid gametophytes bearing sex organs. In mosses the gametophyte is the dominant plant and the sporophyte is the spore-bearing capsule
alternitepalous (L. alternus: one after the other; Gr. skepas: covering; [pe]talon: leaf) adj. Describes floral parts, inserted alternately with the tepals. With the stamens positionned between the petals or corolla lobes.
altherbosa (L. altus: tall, high; herba: plant, herb) n. Communities with tall herbaceous plants, especially in denuded forest areas.
altruism n. In animal behaviour, an act or activity that appears to benefit another individual, usually a closely related family member. For example, when the nest or young of some ground-nesting birds are threatened by a predator, the parents will attempt to attract the attention of the predator by feigning injury. Such behaviour is now recognized by evolutionary biologists as promoting the survival of certain combinations of genes. Thus the parent bird might be promoting the survival of copies of its genes in its offspring, despite putting itself at risk.
alutaceous (L. alutacius: made of soft leather) adj. Leathery. Of pale brown color; leather-yellow.
alvar n. A Swedish term for a habitat type consisting of dwarf shrubs. A biological environment based on a limestone plain with thin or no soil and, as a result, sparse vegetation. This challenging habitat supports a community of rare plants and animals. Trees and bushes are absent or severely stunted.
alveola (L. alveolus: small bowl) n. (pl. alveolae, alveolas) A pit on the surface of an organ. Pits arranged in a honeycomb-like pattern; a small cavity, pit, or hollow. Syn. alveolus.
alveolae See alveola.
alveolar See alveolate.
alveolate (L. alveolatus: pitted as a beehive) adj. Deeply pitted so as to resemble a honeycomb, as are the surfaces of some seeds or achenes, sometimes applied to spores, e.g., species of Fossombronia. Cf. foveolate, areola.
alveole See alveola.
alveoli See alveola.
alveolus (pl. alveoli). See alveola.
amanita (Gr. amanitês: a kind of mushroom) n. Any fungus of the genus Amanita, comprised chiefly of poisonous species.
Amanita (Gr. amanitês: a kind of mushroom) n. A genus of widely distributed mushroom fungi (about 100 species). Several species are extremely poisonous, including the deadly destroying angels (A. vena and A. virosa), the death cap, and the fly agaric. Some species are harmless and sometimes eaten, for example panther cap (A. pantherina). Order: Agaricales.
ambit (L. ambitus, the going around) n. The outline of a shape or body; the scope, extent, or bounds of something.
ameba N. (pl. ameba, amebae) See amoeba.
amebic See amoebic.
amenorrhea n. Lack of menarche or cessation of menses.
amensalism n. A symbiotic relationship between organisms in which one species is harmed or inhibited and the other species is unaffected. See also: commensalism.
ament (L. amentum: strap) n. (pl. aments or amenta) Catkin, or scaly spike, i.e. an inflorescence consisting of a dense spike or raceme of apetalous, unisexual flowers, as in Salicaceae and Betulaceae. Syn. amentum.
amenta (L. amentum: strap) See ament.
amentaceous (L. amentum: strap) adj. Ament-like, or ament-bearing.
amentiferous (L. amentum: strap; ferre: to carry) adj. Ament-bearing.
amentula See amentulum.
amentulum n. (pl. amentula) The so-called catkins of the male androecium in Sphagnum.
amentum See ament.
ameristic (Gr. a-:without; meristos: divided) adj. Not divided into parts; having no meristem.
amethystine (L. amethystinus: amethyst-colored) adj. Amethyst-colored; purplish.
amine n. An amino acid with the carboxyl group removed - very smelly!
amino acid Unit molecule from which proteins are constructed by polymerization.
amitosis (Gr. a-: without; mitosis: thread) n. Direct cell division, in which the nucleus simply cleaves in two (sometimes but not always followed by division of the cytoplasm is very rare.
ammonification n. The formation of ammonia compounds from organic materials containing nitrogen, i.e. the production of ammonia or ammonium compounds in the decomposition of organic matter, especially through the action of bacteria. The Impregnation with ammonia or an ammonium compound.
ammonite n. A member of the Family of Ammonoidea.
ammonites n. Members of the Family of Ammonoidea.
Ammonoidea n. Subclass of cephalopods which generally have planispirally coiled, septate shells (see septum). Characteristically the shells are tightly coiled and planispiral, although some are coiled loosely or spirally; the protoconch is globular; the shells may be either involute or evolute. Some forms have marked ventral keels; ribs and nodes may also be present. The siphuncle is variable but mainly ventral in position. Sutures are often very complex. camaral deposits are absent. The Ammonoidea were probably tetrabranchiate (four-gilled) cephalopods. They constitute the largest cephalopod subclass, with 163 families including the ammonites, in which the suture lines form very complex patterns; the ceratites, in which part of the suture line is frilled; and the goniatites, with relatively simple suture lines. They range in age from Devonian to Upper Cretaceous. All members are now extinct.
ammophilous adj. sand-loving.
amnion n. The liquid surrounding an embryo while in uterus or in an egg. Also amniotic fluid, amniotic waters. Also amnios.
amnios See amnion.
amniotic fluid See amnion.
amniotic waters See amnion.
amoeba (Gr. amoibê: change, alternation) n. A member of the genus Amoeba.
Amoeba (Gr. amoibê: change, alternation) n. A genus of protoctists (see also protozoa) of the phylum Rhizopoda, members of which have temporary body projections called pseudopodia. These are used for locomotion and feeding and result in a constantly changing body shape (see amoeboid movement). Most species are free-living in soil, mud, or water, where they feed on smaller protoctists and other single-celled organisms, but a few are parasitic. The best known species is the much studied A. proteus.
amoebic (Gr. amoibê: change, alternation) adj. Of, pertaining to, or ressembling an amoeba.
amoeboid (Gr. amoibê: change, alternation; eidô: to look like) adj. Ressembling or related to amoeba.
amoeboid movement A type of cell locomotion in which a change of state of regions of the cytoplasm between a viscous gel form and a more liquid sol form results in a flow of the cell's contents, producing movement. It is characteristic of Amoeba, a genus of protoctistans, though it also occurs in a wide range of other cells including certain leucocytes in humans.
amorphic See amorphous.
amorphous (Gr. a-: without; morphê: shape) adj. Without any definite form; shapeless; lacking symmetry. Syn. amorphic, paleomorphic.
amphi- prefix. Meaning both, complete (the latter as in amphiparacytic, where the subsidiary cells completely surround the stoma).
amphibious (Gr. amphi: around, on both side; bios: life) adj. Living both in water and on land.
amphicarpic See amphicarpous.
amphicarpous (Gr. amphi: around, on both side; karpos: fruit) adj. Producing two types of fruit that differ either in form or in time of ripening; sometimes said of plants which bear more than one crop each year. Also amphicarpic.
amphichiral See achiral.
amphicribral adj. Of vascular bundles with phloem completely surrounding the xylem.
amphidiploid (Gr. amphi: around, on both side; dis: twice: eidos: form) adj., n. Describing an organism, cell, or nucleus that contains diploid sets of chromosomes originating from two different species. Crosses between taxonomically unrelated organisms are usually infertile, principally because the chromosomes lack a partner with which to pair during meiosis. However, if there is doubling of the parental sets of chromosomes, pairing can take place within each set, and meiosis may proceed to produce fertile gametes. For example, the F1 hybrid resulting from a cross between a cabbage (Brassica sp.) and a radish (Raphanus sp.) is sterile. Yet such crosses may produce a few seeds that are capable of germinating into fertile F2 plants. These seeds form following the chance fusion of two unreduced gametes, each of which contain all parental chromosomes. Hence, instead of the 18 chromosomes of the F1 hybrid (nine from each parent), the F2 has 36 chromosomes in its somatic nuclei, and thus contains the full diploid sets of both its progenitor species. During meiosis the chromosomes undergo pairing just like a normal diploid plant, and the result is a generally true-breeding hybrid, named Raphanobrassica. See also allopolyploid. Syn. amphiploid.
amphigastria See amphigastrium.
amphigastrium n. (pl. amphigastria) The underleaves in leafy liverworts; in a few mosses, smaller leaves on the upper (Racopilum) or lower (Helicophyllum) stem surface, variously differentiated from the lateral leaves. Cf underleaf.
amphigean (Gr. amphi: around, on both side; gê: earth) adj. Native of both Old and New Worlds. Extending over all the zones, from the tropics to the polar zones inclusive.
amphigenesis (Gr. amphi: around, on both side; genesis: creation, production) n. The joining of gametes to form a zygote; sexual generation; amphigony.
amphigenetic (Gr. amphi: around, on both side; genesis: creation, production) adj. Refers to an organism or a part of the growth cycle that produces zygotes.
amphigenous (Gr. amphi: around, on both side; gennaô: to produce) adj. Increasing in size by growth on all sides, as the lichens. Of certain parasitic fungi growing on both sides of leaves.
amphihaploid adj., n. A plant having a haploid (1n) set of chromosomes from each parent of an interspecific hybrid, thus being (2x) rather than (4x), as in the case of an amphidiploid.
amphimixis (Gr. amphi: around, on both side; mixis: mixing) n. Sexual reproduction; the union of the sperm and egg in sexual reproduction; the joining of parental characters.
amphiparacytic adj. Of paracytic stomata where the subsidiary cells are parallel to the long axis of the stoma and completely surround the latter. Cf. brachyparacytic.
amphiphloic (Gr. amphi: around, on both sides; phloios: [inner] bark) adj. With phloem on both side; an amphiphloic siphonostele has phloem on both sides of the xylem.
amphiphyte (Gr. amphi: around, on both side; phyton: plante) n. A plant growing in the edge of wetland and water showing amphibious characteristics.
amphiploid (Gr. amphi: around, on both side; eidos: form) n, adj. A variation on polyploid in which there are two sets of chromosomes, each set coming from a different species. Syn. amphidiploid.
amphipolyploid adj., n. A polyploid that arises by the addition of the complete somatic chromosome sets of two or more known species.
amphisarca (Gr. amphi: around, on both side; sarx, sarkos: flesh) A many-seeded indehiscent fruit, as a gourd, having a pulpy interior and a hard, woody rind.
amphistomal adj. When and where the two integuments are at about the same level at the micropyle of an ovule. Cf. bistomal, endostomal, exostomal, naked, zigzag.
amphistomatous adj. With stomata on both sides of a bifacial structure, e.g. a leaf blade.
amphitecia See amphitecium
amphitecium (Gr. amphi: around, on both side; thêkê: box) n. (pl. amphitecia) The layer, or one of the layers of cells in the capsule of a moss surrounding the spores, i.e. the outer layers of cells of the sporangium. Also amphithecium. Cf. endothecium.
amphithecia See amphithecium.
amphithecium n. (pl. amphithecia) See amphitecium.
amphitropous (Gr. amphi: around, on both side; tropos: direction, way) adj. Of an ovule inverted so that the funicule is in the middle of one side.
amphitropous ovule An ovule which is half-inverted and straight, with the hilum lateral.
amphivasal adj. Of vascular bundles, with xylem completely surrounding the phloem. Cf. amphicribral, bicollateral, collateral.
amphora (Gr. amphi: around, on both side; phora: carrying) n. The lower portion of a pyxis.
amphoteric (Gr. amphoterôs: both ways) adj. Refers to the ability of a substance to react either as an acid or a base, an amino acids. Describes something made of two components, or acting like two different components.
amplectant (L. amplector: to surround) adj. Twining around or clasping some other body as a tendril. See amplexicaul.
amplexicaul (L. amplexor: to kiss, clasp; Gr. kaulos: stalk) adj. Clasping the stem, as the base or stipules of some leaves. Also amplexicaulous.
amplexicaulous See amplexicaul.
amplexifoliate (L. amplexor: to kiss, clasp; folium: leaf) adj. Having amplexicaul leaves.
ampliate (L. ampliare: to enlarge) adj. Enlarged or expanded.
ampliation (L. ampliare: to enlarge) n. The process of enlarging or amplifying.
ampule See ampulla.
ampulla (L. ampulla: a small inflated bottle) n. (pl. ampullae) A hollow flasklike organ shaped like a bladder or squat round bottle; e.g., the traps and floats such as those found on the leaves of Nepenthaceae or Utricularia. Also ampule.
ampullaceous (L. ampulla: a small inflated bottle) adj. Swelling out like a bottle or bladder. Also ampullate, ampulliform.
ampulliform (L. ampulla: a small inflated bottle; forma: shape) adj. See ampullaceous.
Amygdalaceae (Gr. amygdalê: almond) n. A plant family bearing fruits that contain a single hard seed.
amygdalaceous (Gr. amygdalê: almond) adj. Belonging or pertaining to the Amygdalaceae, a plant family bearing fruits that contain a single hard seed.
amygdaliform (Gr. amygdalê: almond; L. forma: shape) adj. Shaped like an almond. Also : amygdaloid, amygdaloidal.
amygdaloid (Gr. amygdalê: almond; eidô: to be like) See amygdaliform.
amygdaloidal (Gr. amygdalê: almond; eidô: to be like) See amygdaliform.
amyloid adj., n. (A) starchlike substance. Staining blue, blue-purple, blue-black or reddish in iodine.
amyloplast (Gr. amylos: not milled; plastos; modelled, formed) n. A starch forming granule in plants; leucoplast
anabiosis (Gr. anabiôsis: resurrection) n. Revival of an organism after apparent death, like the resurrection plant, Anastatica. A state of suspended animation, especially one in which certain aquatic invertebrates are able to survive long periods of drought.
anabiotic adj. See anabiosis.
anabolic adj. See anabolism.
anabolism n. The process of building up protoplasm from simple substances. Synthesis as opposed to catabolism.
anacanthous (Gr. an-: without; akantha: thorn, spine) adj. Having no spine or thorns.
anacrogynous adj. Having archegonial production in a lateral position on a stem, branch or thallus, from superficial initials and without loss of apical cell function. Cf. to acrogynous.
anaerobe (L. Gr. an-: without; aêr, aeros: air; bios: life) n. An organism, such as a bacterium, which can survive in the absence of oxygen.
anaerobic (L. Gr. an-: without; aêr, aeros: air; bios: life) adj. Living in the absence of air or free oxygen; pertaining to or caused by th absence of oxygen.
anaerobic respiration Gaseous exchange in which the hydrogen removed from the glucose during glycolysis is combined with an organic ion instead of oxygen; e.g. denitrification, sulfate reduction.
anaerobiosis (L. Gr. an-: without; aêr, aeros: air; bios: life) n. Life in the absence of air or free oxygen; anaerobic respiration, respiration occurring in the absence of oxygen.
anaerophytobionts n. Soil flora which exist without oxygen.
anagensis (Gr. ana: at the top; genesis: origin, source) n. Evolutionary change along an unbranching lineage; change without speciation.
analeptic (Gr. analêptikos: restorative, suited to give strength back) adj. Restoring, invigorating; giving strength after disease.
analgesic (L. Gr. an-: without; algêsis: suffering, pain) n., adj. A substance that reduces pain without causing unconsciousness, either by reducing the pain threshold or by increasing pain tolerance. There are several categories of analgesic drugs, including morphine and its derivatives (see opiate), which produce analgesia by acting on the central nervous system; nonsteroidal anti-inflammatory drugs (e.g. aspirin); and local anaesthetics.
analogous (Gr. analogia: conformity, relation) Of similar function, but of different evolutionary descent, of different phylogenetic origin, as the wings of an insect and those of a bird, as stomata and air-pores. Cf. homologous.
anamorph n. An asexual stage or morph characterised by the production of conidia.
anamorphic adj. Pertaining to the gradual evolution from one type of organism into another.
anamniote See amnion.
anandrous (L. Gr. an-: without; anêr, andros: male, man) adj. Without stamens; lacking an androecium.
ananthous (L. Gr. an-: without; anthos: flower) adj. Without flowers.
anastomose v. To communicate or connect by anastomosis. Also anastomosis.
anastomosed adj. Netted, as veins in a leaf. See anastomosis.
anastomosing adj. Rejoining after branching forming an intertwining network, as in some leaf veins. See anastomosis.
anastomosis (Gr. ana: at the top; stoma, mouth) n. ( pl. anastomoses) A cross-connection of arteries, branches, rivers, etc.; connecting by cross-veins and forming a network, e.g. of veins in a leaf blade; union of one structure with another; interconnecting; sometimes applied to irregularly divided peristome teeth. Also anastomose.
ansulcate adj. Of pollen grains, a common form having an elongate aperture at the distal pole of the grain. Cf. tricolpate, tricolporate.
anatomy (L. anatomia [Gr. anatomê]: dissection) n. The branch of morphology that deals with the structure of plants, esp. the internal structure as revealed by the microscope.
anatropous (Gr. ana: at the top; tropos: direction, way) adj. Turned back on itself. Of an ovule, inverted so that the micropyle faces the placenta.
anatropous ovule An ovule which is inverted and straight with the micropyle situated next to the funiculus; the chalaza being situated at the opposite end.
anauxotelic adj. Describes inflorescences, parts of inflorescences or axes that do not end in a flower, and in which growth does not continue beyond the flowering region. Cf. auxotelic.
ancestor n. Any organism, population, or species from which some other organism, population, or species is descended by reproduction.
anchor-ice n. Frozen water that forms at the bottom of a stream; ice which sometimes forms about stones and other objects at the bottom of running or other water, and is thus attached or anchored to the ground. Anchor ice forms on the seafloor at depths shallower than 33 meters, and most significantly at depths shallower than 15 meters; under the sea ice, anchor ice plays a key role in the shallow benthic ecosystem as a natural physical disturbance.
ancipital (L. anceps, ancipitis: two-headed) adj. Two-edged, as the winged stem of Sisyrinchium.
ancophilous adj. Thriving in steep valleys or canyons.
androclinia See androclinium.
androclinium (Gr. anêr, andros: male; klinê: bed) n. (pl. androclinia) See clinandrium.
androcyte n. A cell that matures into a spermatozoid (antherozoid).
androdioecious (Gr. anêr, andros: male; dyo: two; oikos: house) adj. Having bisexual (i.e. perfect. monoclinous) flowers and staminate (male only) flowers, on separate plants.
andro-dioecious See androdioecious.
androecia See androecium.
androecial adj. Pertaining to the androecium.
androecial branch A specialized branch bearing antheridia.
androecious adj. A plant having staminate flowers (sometimes called all-male). Cf. andromonoecious, dioecious, gynoecious, gynomonoecious, hermaphroditic, monoecious, trimonoecious.
androecium (Gr. anêr, andros: man; oikos: house) n. (pl. androecia) The stamens taken collectively; the male reproductive organs of a plant; a collective term applied to all structures of the stamen whorl or whorls in the flower of a seed plant; the antheridia and surrounding bracts (perigonium or involucre). Cf. gynoecium.
androgametophyte (Gr. anêr, andros: man; gametês: spouse; phyton: plant) n. Male gametophyte. Cf. gynogametophyte, androgynogametophyte.
androgenetic haploid A plant having chromosomes from the male parent only.
androgenous adj. Bearing androecia.
androgonial cell Internal initial of a developing antheridium that gives rise to androcyte mother cells.
androgynal (Gr. anêr, andros: man; gonos, woman) adj. Bearing staminate and pistillate flowers on the same parent stem. See androgynous.
androgynogametophyte (Gr. anêr, andros: man; gynê: woman; gametês: spouse; phyton: plant) n. Autoicous or synoicous gametophyte. See androgametophyte, gynogametophyte.
androgynophore (Gr. anêr, andros: man; gynê: woman; phora: carrying) n. A stalk bearing both the androecium and gynoecium of a flower above the level of insertion of the perianth.
androgynous (Gr. anêr, andros: man; gynê: woman) adj. With stamens and pistils in the same flower or inflorescence. Having staminate flowers above the pistillate flowers in the same inflorescence, as in some Carex species. Cf. gynaecandrous, monoicous.
androgyny n. See androgynous.
andromedotoxin See andromedotoxins.
andromedotoxins n. A class of diterpenes causing poisoning in animals.
andromonoecious (Gr. anêr, andros: man; monos: alone, single; oikos: house) adj. Having bisexual (perfect, monoclinous) and male (staminate) flowers on the same plant. Cf. androecious, dioecious, gynoecious, gynomonoecious, hermaphroditic, monoecious, trimonoecious.
andro-monoecious See andromonoecious, andro-polygamous.
andropetalous (Gr. anêr, andros: man; petalon: leaf) adj. Having petaloid stamens, or petals with a small anther at the apex, as in certain double flowers.
androphore (Gr. anêr, andros: man; phora: carrying) n. A support or column, formed by fusion of filaments, on which the stamens are borne; a stalk bearing the androecium.
andropolygamous (Gr. anêr, andros: man; polys: many, single; oikos: house) adj. See andromonoecious.
andro-polygamous See andropolygamous.
androsporangia See androsporangium.
androsporangium (Gr. anêr, andros: man; spora: seed; aggeion: vase, bowl, container) n. (0l. androsporangia) The receptacle in which androspores are formed.
androspore (Gr. anêr, andros: man; spora: seed) n. The minute reproductive body, which gives rise to the (often exceedingly obscure) male plantlet in the sexual generation. A male spore of Isoëtes.
Anemiaceae n. A family of the phylum Filicinophyta (Pterophyta, Pterodatina, Pteridophyta, ferns).
anemochore (Gr. anemos: wind; khôreô: to move) n. A species in which the action of the wind is used for dissemination. Cf. anemochory.
anemochorous adj. See anemochory.
anemochory (Gr. anemos: wind; khôreô: to move) n. The dispersal of plant seeds by the wind. Also anemochore. Cf. diaspore, disseminule.
anemophilous (Gr. anemos: wind; philos: friend, loved) adj. Pollinated by wind; producing wind-borne pollen. Also anemophious. Cf. anemochory, entomophilous.
anemophily (Gr. anemos: wind; philos: friend, loved) n. Pollination of a flower in which the pollen is carried by the by wind. Examples of anemophilous flowers are those of grasses and conifers, of Fagaceae, Juglandaceae, Betulaceae, etc. Cf. entomophily, hydrophily.
anemotaxis (Gr. anemos: wind; taxis: arrangement) n. The reaction to wind experienced by a free-moving organism; the mechanism by which organisms orient their motion in the direction of the wind. Cf. phototaxis, magnetotaxis, geotaxis, phonotaxis, chemotaxis, rheotaxis.
anemotropism (Gr. anemos: wind; tropos: direction) n, Movement or growth of cells or organisms, e.g. plants, in response to wind.
aneuploid adj., n. Refers to the presence of an irregular number of chromosomes, higher or lower than multiples of the haploid number. Cf. euploid.
anfractuose adj. Tightly twisted together; winding; full of windings and turnings; closely sinuous; tortuous. Also anfractuous
anfractuous See anfractuose.
angiocarp (Gr. aggeion: vessel, bowl, container; karpos: fruit) n. A plant bearing an angiocarpous fruit. See angiocarpous.
angiocarpic See angiocarpous.
angiocarpous (Gr. aggeion: vessel, bowl, container; karpos: fruit) adj. Of a fruit partially or wholly enclosed in a shell, involucre or husk. Also angiocarpic.
angiosperm (Gr. aggeion: vessel, bowl, container; sperma: seed) n. Any flowering plant, i.e. a seed-bearing plant whose ovules, and hence seeds, develop within an enclosed ovary. Angiosperms comprise a vast phylum (or division) of diverse leafy green plants (Anthophyta or Angiospermophyta; about 240 000 species) in which the seeds are formed within an ovary, which becomes the fruit. They are thought to have evolved from the cone-bearing gymnosperms at the end of the Jurassic period (about 135 million years ago), rapidly radiating and becoming the dominant plants in the mid-Cretaceous (about 100 million years ago). They include many trees and shrubs but most are herbaceous. The 300 families are grouped into two classes: the monocotyledons and dicotyledons. Cf. gymnosperm.
Angiospermae (Gr. aggeion: vessel, bowl, container; sperma: seed) n. A major division of the plant kingdom, commonly called flowering plants as their reproductive organs are in flowers, having seeds which develop in a closed ovary made of carpels, a very reduced gametophyte, and endosperm develop from a triple fusion nucleus. Any of a class (Angiospermae) or division (Magnoliophyta) of vascular plants (as magnolias, grasses, oaks, roses, and daisies) that have the ovules and seeds enclosed in an ovary, form the embryo and endosperm by double fertilization, and typically have each flower surrounded by a perianth composed of two sets of floral envelopes comprising the calyx and corolla.
Angiospermophyta (Gr. aggeion, vessel, bowl, container; sperma seed; phyton: plant) See Anthophyta, Magnoliopsida.
angiospermous (Gr. aggeion: vessel, bowl, container; sperma: seed) adj. Related to the angiosperms, i.e. with the seeds developped within an enclosed ovary, i.e. having the seeds borne within a pericarp.
angled (L. angulus: angle) adj. Having evident ridges.
angle of repose The maximum degree of gradient on which soil or loose rock remain stable. Syn. critical slope.
angular See angulate.
angular cells See alar cells.
angulate (L. angulus: angle) adj. Angled; refers to an organ that shows a specific number of angles, e.g., mints, Labiatae, which have stems that are 4-angled, and are square in the cross section. Also angular.
angustate (L. angustus: narrow, cramped) adj. Attenuate; tapering smoothly and concavely to a point.
angustifolia (L. angustus: narrow, cramped; folia: leaf)) Epithet of a species, meaning wit narrow leaves, e.g. Elaeagnus angustifolia, Typha angustifolia.
angustiseptal See angustiseptate.
angustiseptate (L. angustus: narrow, cramped; septum: fence, partition) adj. Said of a fruit flattened at right angles to the septum; said of a fruit the septum of which crosses the narrowest diameter. With narrow partitions. Cf. latiseptate. Also angustiseptal.
aniso- (Gr. anisos: unequal) prefix. Meaning unequal or dissimilar.
anisocytic adj. Of stomata, with three subsidiary cells, two large and one smaller, surrounding the guard cells. Cf. actinocytic, anomocytic, cyclocytic, diacytic, paracytic, staurocytic, tetracytic.
anisogamete n. A gamete of either of two kinds sexually differentiated in size or structure; the condition in which two such kinds of gametes are present.
anisogametic adj. See anisogamete.
anisogamous adj. With gametes of unequal size.
anisogamy n. The copulation of gametes with unlike morphology.
anisogeny The production of ovules and pollen that exhibit a consistent difference in genetic constitution,
anisomerous (Gr. anisos: unequal; meros: part) adj. With a different number of parts (usually less) than the other floral whorls, as in a flower with five sepals and petals, but only two stamens.
anisophyllous (Gr. anisos: unequal; phyllon: leaf) adj. With leaves of different sizes or shape, e.g. Sphagnum, Mittenothamnium, Hypopterygium. Cf. isophyllous.
anisophylly (Gr. anisos: unequal; phyllon: leaf) n. The presence of two kinds of leaves on one plant as in Selaginella and some cedars, Juniperus. Cf. dimorphism.
anisoploid adj., n. An unequal ploidy levels (e.g., 2x and 4x) among progeny of a polyploid cross.
anisosporous adj. Having spores with a bimodal (or multimodal) distribution of size, generally the smaller spores giving rise to male gametophytes; often associated with nanandry. True heterospory (separate microsporangia and megasporangia) does not occur in bryophytes.
anisotomic adj. With unequal branching, with a distinct main axis and smaller side branches.
annotinal (L. annotinus: of one year; of last year) adj. Appearing yearly.
annotinous (L. annotinus: of one year; of last year) adj. Dsplaying yearly growth, frequently evident by periodic clusters of leaves along a stem; e.g., Polytrichum, Hylocomium splendens.
annual (L. annualis: of the year) adj. Said of a plant which completes its life history within a year. Cf. ephemeral.
annual production The amount of yield each year by an organism or group.
annual ring The layer of wood produced by a single year's growth of a woody plant.
annual seasons The major climatic periods of each year: vernal, estival, autumnal, and hibernal.
annual succession The routine occurrence of plants and animals in an area during each year, such as spring bulbs being replaced by annual flowering plants, and subsequently replaced by autumn perennial flowering plants.
annual turnover The total accumulation of living organisms produced in one year for a certain area. Cf. biomass.
annular (L. annulus: finger ring) adj. In the form of a ring; with the leaves or branches arranged in a circle, e.g., Rhodobryum, Philonotis.
annular thickenings Ring-like thickenings extending over both tangential and radial cell walls, e.g., liverwort capsules.
annulate (L. annulus: finger ring) adj. In the form of a ring; with rings or ringlike markings. Also annulated.
annulated See annulate.
annuli See annulus.
annulus (L. annulus: finger ring) n. (pl. annuli) A ragged ring of tissue that remains on the stalk of a mushroom or toadstool; also called a velum, it is formed from the ruptured membrane that originally covered the lower surface of the cap. Syn. velum. The region of the wall of a fern sporangium that is specialized for spore dispersal; it consists of cells that are thickened except on their outer walls; on drying out, the cells contract and the sporangium ruptures, releasing the spores; the annulus springs back into position when the residual water in the cells vaporizes and any remaining spores are dispersed. In stegocarpous mosses a zone of variously differentiated cells between the capsule urn and operculum, facilitating opening of the capsule. Cf. valve.
anodic adj. The ascending direction of apical cell segmentation; applied to the rectangular merophyte surface that is oriented towards the segmentation spiral. Cf. to kathodic.
anodyne adj., n. Capable of soothing or eliminating pain; relaxing. A medicine, such as aspirin, that relieves pain. See also anodynes.
anodynes n. Agents which relieve pain, either by impairing the conductivity of the sensory nerve fibres, or by depressing the cerebral centres of perception and sensations. Opium does both, and hence it is the most efficient of all the analgesics. The General Anodynes (Opium, Morphine, Atropine, Antipyrin, etc.) act when taken internally, and affect the whole organism; the Local Anodynes (Opium, Cocaine, etc.) affect the part to which they are applied.
anomalicidal capsule A dry fruit which dehisces irregularly; rupturing capsule.
anomalous adj. A term of convenience, kinds of secondary growth that differ from the ordinary ones.
anomocytic adj, Of a stomata lacking subsidiary cells surrounding the guard cells. Cf. actinocytic, anisocytic, cyclocytic, diacytic, paracytic, staurocytic, tetracytic.
anomocytic stomate A stomate lacking differentiated subsidiary cells.
anorexia (Gr. orexe: appetite) n. The decreased sensation of appetite. While the term in non-scientific publications is often used interchangably with one of its subtypes, anorexia nervosa, there are many possible causes for a decreased appetite, some of which may be harmless while others pose significant risk for the person.
anoxia (Gr. an-: without; oxys: acute) n. Lack of oxygen or not enough oxygen.
anoxic (Gr. an-: without; oxys: acute) adj. Greatly deficient in oxygen.
antagonism n. The depressive effect of one organism upon another, such as certain grasses like timothy hay on the production of alfalfa hay.
antarctic (Gr. anta: opposite, vis-à-vis; arktikos: arctic, northern) adj. Distributed in those regions ofthe earth lying between the Antarctic Circle and the South Pole.
antasthmatic adj., n. Opposing, or fitted to relieve, asthma. A remedy for asthma.
ante- prefix. Meaning in front of, e.g. antepetalous inserted in front of (adaxially to, opposite) the petals, antesepalous, inserted in front of the sepals.
antecedent moisture The degree of liquid which has soaked into the soil at the start of the runoff period.
antemarginal (L. ante: in front of; margo, marginis: edge) asj. Inside of, or not extending quite to the margin.
antepetalous (Gr. anti: in front of; petalon: leaf) adj. Directly in front of (opposite) the petals.
anterior (L. anterior: that is in front) adj. Away from the stem, midrib, pistil or other organ; e.g. on a lipped flower, the bottom lip is anterior, the top lip is posterior; sometimes the anterior lip is less correctly called inferior or exterior; said of floral organs on the side of the flower farthest from the axis; in transversely inserted leaves, the side or surface oriented away from the axis. Cf. posterior.
anterolateral See antero-lateral.
antero-lateral (L. anterior: that is in front; lateralis: of the side) adj. In front and on the sides.
antesepalous (Gr. anti: in front of) adj. Directiy in front of (opposite) the sepals.
anthela (Gr. anthos: flower) n. An inflorescence with lateral flowering branches exceeding the main axis, as in some species of the genus Juncus.
anthelate (Gr. anthos: flower) adj. With the inflorescence in the form of an anthela.
anthelmintic (Gr. anti: against; elmins, elmintos: intestinal worm, helminth) adj., n. (Of) medicines or drugs that can destroy or expel intestinal worms.
anthemia (Gr. anthos: flower) See anthemy.
anthemy (Gr. anthos: flower) n. A flower-cluster.
anther (Gr. anthêros: flowered) n. The top (apical portion) of the stamen, usually elevated by means of a filament, which contains the pollen, i.e. the polliniferous part of a stamen.
anther sac A pocket-shaped unit containing pollen. In many plants, the anther has two lobes, each with two pollen sacs.
antheridia See antheridium.
antheridial adj. Related to the antheridium.
antheridiophore (Gr. anthêros: flowered; phora: carrying) n. Specialized antheridium bearing branch, e.g. Marchantia.
antheridium (Gr. anthêros: flowered) n. (plural antheridia) The fertile organ of a male gametophyte or the male organ of a bisexual gametophyte, i.e. the male sex organ of cryptogams (algae, fungi, bryophytes, clubmosses, horsetails, and ferns) borne on the prothallium. It produces the male gametes (antherozoids). It may consist of a single cell or it may have a wall that is made up of one or several layers forming a sterile jacket around the developing gametes. The antheridium in cryptogams corresponds to an anther in flowers. Male gametangium; a multicellular globose to broadly cylindric, stalked structure containing spermatozoids. Syn. androgonium. Cf. archegonium.
antheriferous (Gr. anthêros: flowered; L. ferre: to carry) adj. Anther-bearing; containing anthers.
antheroid (Gr. anthêros: flowered; eidô: to be like) adj. Similar to an anther.
antherozoid (Gr. anthêros: flowered; zôon: any living being; eidô: to be like) n. The motile male gamete of algae, fungi, bryophytes, clubmosses, horsetails, ferns, and certain gymnosperms. Antherozoids usually develop in an antheridium but in certain gymnosperms, such as Ginkgo and Cycas, they develop from a cell in the pollen tube. Syn. spermatozoid.
anthesis (Gr. anthêsis: flowering) n. Stage or period during which the flower bud is fully open; the time of opening of a flower. Syn. sponsalia.
anthesmotaxis (Gr. anthos: flower; taxis: arrangement) n. The arrangement of the various flower parts.
anthocarp (Gr. anthos: flower; karpos: fruit) n. A false fruit consisting of the true fruit and the base of the perianth, as in Nyctaginaceae. A fruit with some portion of the flower besides the pericarp persisting, as in a pome with the fleshy perianth tube surrounding the pericarp. A pseudocarp consisting of the true fruit and the base of the perianth.
anthocarpous (Gr. anthos: flower; karpos: fruit) adj. Of a fruit having accessory or enlarged tissue, as the appel or straberry. Of or pertaining to anthocarps; bearing anthocarps. See anthocarp.
Anthocerophyta (Gr. anthos: flower; keras: horn; phyton: plant) n. A phylum comprising about 100 species of simple nonvascular plants, the hornworts (or horned liverworts), found worldwide in temperate and tropical regions on tree trunks, riverbanks, and other damp locations. They resemble thallose liverworts (see Hepatophyta), but produce long horn-shaped green sporophytes, which split longitudinally to release the spores. Hornwort cells each contain a single chloroplast inside which, uniquely among plants, is a pyrenoid, associated with starch production. Some species have separate male and female plants, while others have both types of sexual organ on the same plant. The motile sperm swim through the surface water film to fertilize the female gametes, and the resultant embryo gives rise to young sporophytes. Young gametophytes arise directly from the germinating spores. Hornworts were formerly classified as a class (Anthocerotae) of the Bryophyta.
anthochlor See anthochlors.
anthochlors See chalcones.
anthocyanic adj. Containing anthocyanin pigments.
anthocyanidin See anthocyanidins.
anthocyanidins n. A class of coloured anthocyanin aglycones formed from flavan-3,4-diols, also when proanthocyanidins are hydrolyzed with acid (note that they are not formed from proanthocyanidins in the plants).
anthocyanin (Gr. anthos: flower; kyaneos: dark-blue) n. One of a group of water-soluble glycosidic flavonoid pigments. Anthocyanins occur in plants, particularly in the vacuoles of flowers, fruits and leaves. The colour of anthocyanins depends on pH, but they are commonly responsible for the red, purple and blue pigmentations of petals. the blue, red, and purple colours in plants (particularly in flowers).
anthocyanins See anthocyanin.
anthodia See anthodium.
anthodium n. (pl. anthodia) A flower head or capitulum, especially the head of a composite plant.
anthophore (Gr. anthos: flower; phora: carrying) n. An elongated stalk (stipe), produced by th elongation of the internode between the calyx and the corolla, bearing the corolla, stamens, and pistil above the receptacle and calyx.
Anthophyta (Gr. anthos: flower; phyton: plant) n. A phylum comprising the flowering plants (angiosperms). The gametes are produced within flowers and the ovules (and the seeds into which they develop) are enclosed in a carpel (Cf. Coniferophyta). The angiosperms are the dominant plant forms of the present day. They show the most advanced structural organization in the plant kingdom, enabling them to inhabit a very diverse range of habitats. There are two classes within this group: the Monocotyledonae with one seed leaf (cotyledon) in the seed, and the Dicotyledonae with two seed leaves.
anthophyte (Gr. anthos: flower; phyton: plant) n. A flowering plant, or any of its closest relatives, such as the Bennettitales, Gnetales, or Pentoxylales.
anthotaxy (Gr. anthos: flower; taxis: arrangement) The arrangement of flowers on the flowering axis; inflorescence.
anthoxanthin See anthoxanthins.
anthoxanthins n. Yellow, cream or colorless flavonoids occuring in cell saps.
anthracine (Gr. anthrax: coal) adj. Coal-black
anthracnose (Gr. anthrax: coal; nosos: sickness) n. A general term describing some plant diseases. It may for instance refer to a fungus (Colletotrichum), or to Gnomoniella fraxini that causes ash anthracnose, etc.
anthraquinone See anthraquinones.
anthraquinones n. Quinones in which the aromatic ring is fused to both sides of a benzoquinone ring, occuring as glycosides in plants, often colored.
anthropochore (Gr. anthrôpos: human being; khôreô: to move) n. A species in which the chief force for dissemination is human activity, Cf. anthropochory.
anthropochorous (Gr. anthrôpos: human being; khôreô: to move) adj. Of plants that are distributed by the action of man.
anthropochory (Gr. anthrôpos: human being; khôreô: to move) n. Dispersal of organisms, such as seeds, as a result of human activity. Cf. anemochory.
anthropogenic (Gr. anthrôpos: human being; gennaô: to produce) adj. Refers to something originating from humans and the impact of human activities on nature. Also anthropogenous.
anthropogenous See anthropogenic.
anthropophilous (Gr. anthrôpos: human being; philos: loved, friend) adj. Refers to plants which grow near humans and their dwellings, such as dooryard violet, Viola odorata.
anti- (Gr. anti: in front of, against; L. ante : before) prefix. Meaning against, opposed to or before.
antiallergenic (Gr. anti: against; allos: other; ergon: action) adj. Refers to herbal medicines that can reduce or relieve allergic reactions.
antiaphrodisiac (Gr. anti: against; aphrodisiakos: that concerns sexual desire) adj. Refers to herbal medicines that can reduce sexual desire.
antiasthmatic adj., n. Same as antasthmatic.
antibacterial adj., n. (A product) destroying or inhibiting the growth of bacteria.
antibiosis (Gr. anti: against; bios: life) n. The reaction, often death or sterilization, produced in organisms by an antibiotic. In general, the creation of metabolic byproducts that are toxic to other organisms. For example, during the decomposition process, bacterial reactions produce substances that are toxic to most pathogens.
antibiotic (Gr. anti: against; bios: life) adj. Substance that slows the growth or multiplication of, or kills, a living organism; usually referring to bacteria.
antical adj. Of the dorsal surface of a stem; the leaf margin oriented towards the shoot apex of a longitudinal or obliquely inserted leaf. Cf. to postical.
anticonvulsant n. A diverse group of pharmaceuticals used in the treatment of epileptic seizures. They are also increasingly being used in the treatment of bipolar disorder, since many seem to act as mood stabilizers. Also anticonvulsive.
anticonvulsive n. See anticonvulsant.
anticlinal (Gr. antiklinô: to tilt the opposite way) adj. Perpendicular to the surface; radial; at right angles to the free or exposed surface; applied to cell divisions that are perpendicular to the free surface. Cf. to periclinal, transverse.
anticline (Gr. antiklinô: to tilt the opposite way) n. A geological structure or arch formed by strata from opposite sides rising upward in a common line. Cf. syncline.
antidiarrheal adj. See diarrhea.
antifungal (Gr. anti: against; L. fungus: mushroom, fungus) adj., n. Destroying or inhibiting the growth of fungi.
antihemorrhagic adj. Tending to stop hemorrhage. n. A remedy for hemorrhage.
antihistamine n. Herbal or other medicines that can neutralize the effect or inhibit production of body histamines, and used chiefly in the treatment of allergic disorders and colds. Drug which block the action of histamine, thus preventing or alleviating the major symptoms of an allergic response. Antihistamines are typically combined with a decongestant to help relieve nasal congestion. Cf. histamine.
antihistaminic adj. See antihistamine.
anti-inflammatory (Gr. anti: against; L. inflammatio: inflammation) adj., n. Refers to herbal or other medicines that can ease or neutralize swelling, heat, and pain. Over-the-counter drugs such as aspirin, ibuprofen, ketoprofen and naproxen as well as being analgesics, also have anti-inflammatory properties.
antimicrobial (Gr. anti: against; mikros: small; bios: life) adj. Refers to herbal or other medicines that can slow the growth or multiplication of microorganisms, or kill them.
antineoplastic adj. Realted to any of several drugs that control or kill neoplastic cells; used in chemotherapy to kill cancer cells; all have unpleasant side effects that may include nausea and vomiting and hair loss and suppression of bone marrow function. Acting to prevent, inhibit or halt the development of a neoplasm (a tumor). An agent with antineoplastic properties. For example, oxaliplatin (Eloxatin) is an antineoplastic used in the treatment of metastatic colon cancer.
antiperiodic adj. Preventing regular recurrence of the symptoms of a disease, as in malaria.
antipetalous (Gr. anta: vis-à-vis; petalon: leaf) adj. Inserted in front of the petals; opposite the petals. Syn. antepetalous.
antiphlogistic adj. Reducing inflammation or fever; anti-inflammatory.
antipodal See antipodals.
antipodal cells. See antipodals.
antipodals n. Cells, commonly three in number as in the eight-nucleate embryo sac, located at the other end of the embryo sac from the female gamete, more or less persistent, multiplicative or not.
antipyretic adj.; n. Relieving or reducing fever. An agent that so acts.
antiraphe adj., n. On the other side of the ovule to the raphe.
antiscorbutic n. Refers to medicines and drugs that are efficacious against scurvy, i.e. that provide Vitamin C.
antiscorbutics n. Medicines and drugs that are efficacious against scurvy, i.e. that provide Vitamin C.
antisepalous (Gr. anta: vis-à-vis) adj. Inserted in front of the sepals; opposite the sepals. Syn. antesepalous.
antiseptic adj.; n. (A substance) that inhibits the growth and reproduction of disease-causing microorganism.
antispasmodic (Gr. anti: against; spasmos: spasm, convulsion) adj., n. Refers to medicines or drugs that can relieve cramping or spasms. Also spasmolytic.
antispasmodics (Gr. anti: against; spasmos: spasm, convulsion) n. Medicines or drugs that can relieve cramping or spasms.
antitropous adj. Of the curvature of an ovule with respect to the carpel margin that bears it, curvature in the opposite direction to the curvature of the margin. cf. syntropous, apotropous, epitropous.
antitumor (Gr. anti: against; L. tumor: swelling) adj., n. Counteracting or preventing the formation of malignant tumors; anticancer. Medicine or drug that can prevent or be effective in removing tumors.
antitumoral adj. See antitumor.
antitussive (Gr. anti: against; L. tussid: cough) adj., n. Refers to medicines or drugs that can prevent or ease coughing.
antiviral (Gr. anti: against; L. virus: slime, juice, poison, venom) n. Refers to herbal or other medicines that can slow the growth or multiplication of viruses, or kill them.
antrorse (L. introrsum: towards inside) adj. Directed or bent forward or upward. Cf. retrorse.
antrorsely adv. See antrorse.
aperient adj., n. Gently stimulating evacuation of the bowels; laxative. A mild laxative.
aperiodic adj. See aperiodicity.
aperiodicity (Gr. a-: without; periodikos: periodic) Irregular occurrence of various phenomena, such as leaves dropping out of season (in summer rather than autumn) due to unexpected climatic changes, i.e., storms, droughts, etc. Cf. periodicity.
aperturate (L. apertus: open) adj. Of a spore with one or more pores in the exine.
aperture (L. apertus: open) n. An opening or hole.
apetalous (Gr. a-: without; petalon: leaf) adj. Having flowers without petals; having no corolla.
apex (L. apex: tip, summit) n. (pl. apexes or apices) The tip or summit of an organ; the uppermost point; the narrowed or pointed end; the point farthest from the point of attachment.
apexes See apex.
apheliotropic (Gr. a-: without; êlios: sun; tropos: direction, way) adj. Turning or grawing away form the sun.
aphyllophorale adj. Without gills (of mushrooms).
Aphyllophorales n. An order of mushrooms.
aphotic (Gr. a-: without; phos, photos: light) adj. Having no light. Of or relating to the region of a body of water that is not reached by sunlight and in which photosynthesis is unable to occur.
aphotic zone The deeper portions of bodies of water in which sunlight does not penetrate with enough intensity to cause changes in organisms. Cf. disphotic zone, euphotic zone, photic zone.
aphrodisiac adj., n. An herbal preparation, drug, etc., that can stimulate sexual desire; arousing sexual desire.
aphyllopodic (Gr. a-: without; phyllon: leaf; pous, podos: foot) adj. Having the lowermost leaves reduced to small scales. Cf. phyllopodic.
aphyllous (Gr. a-: without; phyllon, leaf) adj. Without leaves, leafless.
aphyllus (Gr. a-: without; phyllon, leaf) Epithet of a species, meaning without leaves, e.g. Asparagus aphyllus.
aphytal zone The deeper portion of a lake bottom that lacks plants, including the sublittoral zone and the profundal zone.
apical (L. apex, apicis: tip, summit) adj. Relating to the tip; at the tip or summit of an organ, farthest from the point of attachment, as a bud which terminates a stem. Describing the cells composing the apex of the leaf. They are often broader and shorter than the cells of the middle of the leaf.
apical cell A single meristematic cell at the apex of a shoot, thallus, leaf or other organ that divides repeatedly to form new cells.
apical dominance Inhibition of the growth of lateral buds in a plant by the presence of a growing apical bud. It is brought about by the action of auxins (produced by the apical bud) and abscisic acid.
apical lamina In Fissidens the part of the leaf above or distal to the vaginant and dorsal laminae.
apically adv. See apical.
apical meristem A region at the tip of each shoot and root of a plant in which cell divisions are continually occurring to produce new stem and root tissue, respectively (see meristem). The new tissues produced are known collectively as the primary tissues of the plant. See ground meristem; procambium; protoderm. Cf. cambium.
apical notch The marginal indentation in which the apical cell is located in thalloid hepatics; provides an emarginate appearance to the thallus apex; e.g. Metzgeria.
apices See apex.
Apicomplexa n. A phylum of parasitic protoctists (see also protozoa) whose members may have a number of different animal hosts. Their complex life cycle involves the alternation of asexual reproduction (multiple fission) and sexual reproduction and the production of resistant spores. The phylum includes the agents causing malaria (Plasmodium) and toxoplasmosis (Toxoplasma). See Sporozoa.
apicula See apiculum.
apiculate (L. apex, apicis: tip, summit) adj. Terminated abruptly by a small, sharp, slender, flexible, distinct point (mucronate is shorter; cuspidate is longer and stouter).
apicule See apiculus.
apiculi See apiculus.
apiculum (L. apex, apicis: tip, summit) n. (pl. apicula) A short, abrupt, flexible tip.
apiculus (L. apex, apicis: tip, summit) n. (pl. apiculi) A short sharp point, not rigid, at the tip of a leaf, bract or petal. Also apicule.
apigenin n. A deoxyanthocyanin occurring in leaves and flowers.
apo- (Gr. apo: away) prefix. Meaning away from, separate.
apocarp (Gr. apo: away; karpos: fruit) n. A gynoecium having separate carpels. A gynoecium with two or more free standing carpels.
apocarpous (Gr. apo: away; karpos: fruit) adj. Of or pertaining to apocarps; with separate carpels. Of a gynoecium, consisting of two or more carpels which are free from one another or almost so. Cf. syncarpous.
apocarpy (Gr. apo: away; karpos: fruit) n. The condition in which the female reproductive organs (carpels) of a flower are not joined to each other. It occurs, for example, in the buttercup. Cf. syncarpy.
apogameon n. A species that contains both apomictic and non-apomictic individuals.
apogamous (Gr. apo: away; gamos: marriage) adj. Development of a sporophyte from a gametophyte without fertilization. Syn. apomictic. See apogamy.
apogamy (Gr. apo: away; gamos: marriage) n. The formation of a sporophyte directly from a gametophyte by asexual means such as budding, rather than by sexual fertilization; such sporophytes have the same chromosome number as the gametophyte from which they have been derived. Cf. apospory, dipiospory.
apogeotropic See ageotropic, apogeotropism.
apogeotropism n. The response by an organism of turning away from the earth, e.g., plant stems growing upward; negative geotropism. Apogeotropic roots are roots that grow upwards to the soil surface (other roots grow downwards), emerging from the soil and growing upwards. The sego palm has apogeotropic roots, as do cycads.
apolar spore A spore with no distinct polarity, e.g. spores lacking a conspicuous triradiate ridge or pore (opposed to polar spore.
apomict (Gr. apo: away; mixis: mixing) n. A plant that produces viable seed asexually, without fertilisation. See apomixis.
apomictic (Gr. apo: away; mixis: mixing) adj. Of a development by asexual reproduction. Syn. apogamous. See apomixis.
apomixis (Gr. apo: away; mixis: mixing) n. In general, reproducing without sexual reproduction; often used to denote seed production without a sexual process having been involved. A reproductive process in plants that superficially resembles normal sexual reproduction but in which there is no fusion of gametes. In apomictic flowering plants there is no fertilization by pollen, and the embryos develop simply by division of a diploid cell of the ovule. Defined broadly as any form of asexual reproduction and narrowly, and more commonly, as seed production without fertilization. Syn. agamospermy. Cf. apogamy, parthenocarpy; parthenogenesis. Sexual embryos result from the union of male and female gametes, which produces genetically varied offspring. In contrast, apomictic embryos are formed without paternal contribution. Therefore, apomictic offspring carry the full genetic constitution of the mother and form a stable clone, a feature of great value for plant breeding and seed production.
apomorph (Gr. apo: away; morphê: shape) n. An evolutionarily advanced ('derived') character state. The long neck of the giraffe is apomorphic; the short neck of its ancestor is plesiomorphic.
apomorphic (Gr. apo: away; morphê: shape) adj. Applied to features possessed by a group of biological organisms that distinguish those organisms from others descended from the same ancestor. The term means 'new-featured' and refers to 'derived' characters that have appeared during the course of evolution. See apomorph.
apomorphy (Gr. apo: away; morphê: shape) n. When a derived character or trait is inferred to be a modified version of a more primitive condition of that character and therefore inferred to have arisen later in the evolution of the clade. See apomorph, apomorphic.
apopetalous (Gr. apo: away; petalon: leaf) adj. Having separate petals. Also polypetalous. Cf. sympetalous, gamopetalous.
apophyllous adj. Said of whorled flowers with distinct sepals and petals.
apophysis (Gr. apo: away; physis: production) n. (pl. apophyses) A projection or protuberance; that portion of a cone scale that is exposed when the cone is closed; a strongly differentiated, sterile neck at the base of a capsule, between seta and urn, e.g. Trematodon, Polytrichum, Splachnum. Cf. hypophysis, neck.
apoptosis n.The programmed cell death.
aporphine alkaloids n. A group of isoquinoline alkaloids.
aposepalous (Gr. apo: away; skepas: covering, shelter; [pe]talon: leaf) adj. With separate petals, not united to other petals; chorisepalous.
aposporic See aposporous.
aposporous adj. See apospory. Also aposporic.
apospory (Gr. apo: away; spora: seed) n. Development of gametophytes directly form a sporophye, from somatic cells, i.e. without meiosis or spore formation; such gametophytes have the same chromosome number as the sporophyte from which they have been derived. Cf. apogamy, diplospory.
apostapetalum n. Referring to that part of the corolla tube and lobes above the zone with fused or adnate stamens. Cf. stapetalum.
apostemonous (Gr. apo: away; stêmôn: thread) adj. With separate stamens.
apothecia See apothecium.
apothecial adj. Of or relating to the apothecium of some lichens and musrooms.
apothecium (Gr. apo: away; thêkê: box, case) n. (pl. apothecia) The fruit of certain fungus and lichens, usually an open, saucer-shaped or cup-shaped body, the inner surface of which is covered with a layer that bears asci.
apotracheal adj. Of axial parenchyma, parenchyma not associated with the vessels. Cf. paratracheal.
apotropous adj. Of the curvature of an ovule with respect to the ovary axis, abaxial. Cf. epitropous, pleurotropous. see also antitropous, syntropous.
appendage (L. appendere: to hang on, suspend) n. A structure attached to or arising from a larger structure. A subordinate or derivative body part; especially: a limb or analogous part (as a seta). A projecting part of a structure.
appendicula n. (pl. appendiculae) Short transverse projections formed from horizontal wall-pairs, often borne on endostomial cilia (see trabecula); sometimes used in liverworts for the presence of cilia, auricles or other appendages at leaf bases.
appendiculae See appendicula.
appendiculate adj. Having small appendages; forming an appendage. Appendiculate leaf, a small appended leaf; with short, thin, transverse projections.
appendix n. The long narrow development of the spadix in Araceae.
applanate adj. Flattened.
apposition n. In cell wall formation, growth by deposition of layer after layer of wall material. Cf. intussusception.
appressed (L. appressus: pressed against) adj., adv. Pressed closely against but not united with. Lying flat or close against something, as a bud against a twig; leaves appressed against the stem. Often used for hairs.
approximate (L. approximare: to come close) adj. Borne close together, but not fused, leaves that come near each other but do not overlap.
apterous (Gr. a-: without; pteron: wing) adj. Of seeds or fruits: having no winglike expansions, wingless.
apud The connector term used between names when two authors describe the same species in separate publications, e.g., Ceratozamia latifolia Miq. apud Tijdschr.
apyrene (Gr. a-: without; pyrên: stone, pit) adj. Seedless.
aquafer See aquifer.
aquatic (Lat. aqua: water) adj., n. Growing or living in or near water; living in water either free-floating or affixed. An aquatic plant.
aquatic plants Plants that must grow in water whether rooted in the mud or floating without anchorage; plants that must complete part or all of their life cycle in or near the water.
aquatic vascular plants Aquatic plants containing the conductive vascular tissue, phloem and xylem.
aquifer n. A natural holding tank of porous rock or soil locked between impermeable layers in which water may travel long distances. Also aquafer.
aquiherbosa n. Communities of herbaceous plants growing in ponds and marshes.
aquiprata n. Communities of plants where the surface water is a necessary factor, as in wet meadows.
arabinose n. An aldopentose epimeric with ribose at the 2 carbon, occurring naturally in both D- and L-forms, widely distributed in the form of complex polysaccharides, glycosides, and mucilages; arabinoside is a glycoside of arabinose and occurs widely in plant species as a component of sugars, also in gum arabic.
arabinoside n. A glycoside of arabinose and occurs widely in plant species as a component of sugars, also in gum arabic.
arachnoid (Gr. arakhnê: spider, cobweb; eido, to ressemble, to be like or similar to) adj. Like a cobweb; covered with or consisting of soft fibers or hairs so entangled as to give a cobwebby appearance. Also arachnose, araneose, araneous.
arachnose adj. See arachnoid.
araloside n. A triterpenoid saponin. A potent inhibitor of gastric lesion and ulcer formation in rats that was isolated from the root bark of Aralia elata through a bioassay-guided separation procedure.
araneose See arachnoid.
araneous See arachnoid.
arboreal (L. arbor: tree) adj. Of, living in, growing on, or connected with trees; treelike. Cf. arborescent.
arboreous (L. arbor: tree) adj. Wooded; abounding in trees; arboreal; living in or among trees. See arborescent.
arborescent (L. arborescere: to become tree) adj. Resembling a tree (applied to non-woody plants attaining tree height and to shrubs tending to become tree-like in size). Cf. dendroid.
arboretum (L. arboretum: orchard) n. A plot of land where different trees are grown for study or display.
arbuscula (L. arbuscula: shrub, bush) n. A shrub with a tree-like form.
arbuscular adj. Like a small tree; applied to hairs and the complex intrusions of hyphae into the cells in arbuscular and vesicular-arbuscular mycorrhizae.
arbuscular mycorrhiza An endomycorrhizal association between a fungus and a plant root where the fungal hyphae form coils or arbuscules or arbusculate coils within the plant cell.
arbutin n. A benzoquinone.
Archaea (Gr. arkhaios: old) n. The domain comprising what were formerly known as the archaebacteria. What used to be the kingdom Archaebacteria has been split into two kingdoms: Crenarchaeota and Euryarchaeota. The domain Archaea contains the phenotypes: methanogens, sulphate-reducing organisms, and extremophiles.
Archaean n. One of the three subdivisions of the Precambrian, lasting from about 4000 to about 2500 million years ago. Also Archean.
archaeophyte A plant that existed in prehistoric times.
archaeozoic See Archaeozoic.
Archaeozoic (Gr. arkhaios: old; zôon: any living being) adj. Noting or pertaining to a period of the Precambrian era, occuring from on billion to perhaps 3 billions years ago, during which the earliest datable rocks were formed and the earliest known life, algae and fungi, came into being. See Archaean.
Archean See Archaean.
archegone (Gr. arkhê: origin; gonos: generation) n. The egg cell produced in the archegonium.
archegonia See archegonium.
archegoniophore (Gr. arkhê: origin; gonos: generation; phora: carrying) n. A specialized archegonial bearing branch; the female gametangiophore, e.g. Marchantia.
archegonium (Gr. arkhê: origin; gonos: generation) n. (plural archegonia) The multicellular flask-shaped female sex organ of bryophytes, clubmosses, horsetails, ferns, and many gymnosperms. Such plants are described as archegoniate to distinguish them from algae, which do not possess archegonia. The dilated base, the venter, contains the oosphere (female gamete). The cells of the narrow neck liquefy to allow the male gametes to swim towards the oosphere. The archegonium is thus an adaptation to the terrestrial environment as it provides a means for the male gametes to reach the female gamete. Syn. gynogonium. Cf. antheridium, antherozoid, gametangium.
archeozoic See archaeozoic.
archespore (Gr. arkhê: origin; spora: seed) n. The primitive cell, or group of cells, which give rise to the cells from which spores are derived and sometimes elaters. Syn. archesporium. Cf. sporocyte.
archesporia See archesporium.
archesporium (Gr. arkhê: origin; spora: seed) n. (pl. archesporia) See archespore.
archibenthal adj. See archibenthic zone.
archibenthic zone The ocean layers between 200 feet and 3300 feet (65 and 1050 m.); the upper part of the abyssal zone.
archiblast (Gr. arkhê: origin; blasto: bud, sprout) n. The formative part of the egg, as distinguished from the part that nourishes the embryo.
archiblastic (Gr. arkhê: origin; blasto: bud, sprout) adj. Of, pertaining to, or derived form an archiblast.
archicarp (Gr. arkhê: origin; karpos: fruit) n. The female sex organ in various ascomycetous fungi, commonly a pluricellular colied hypha differentiated in a terminal trichogyne and the ascogonium.
arching adj. Curved gently outward and then downward; generally said of stems, large leaves, and floral clusters.
architectural adj. Describes plants that have very strong shapes and are used in landscapes for this reason.
arctic adj. Describes an extremely cold climate, particularly that of the polar regions.
arctic-alpine adj. Refers to areas which are mountainous, above the tree line, and north of the arctic circle.
arcuate (L. arcus: bow) adj. Curved like a bow, like an arch.
arcuately adv. See arcuate.
area n. The total range in which a taxon or community may be found. Cf. basal area, coverage.
arenaceous (L. arena: sand) adj. Growing in sand.
arenicolous (L. arena: sand; colo, colere: to inhabit) adj. Growing in sand or sandy places.
areography n. The study that deals with the range of a species. Cf. area.
areola (L. areola: small yard, small area) n. (pl. areolae, areolas). Any of the spaces between lines on a surface, e.g. of a leaf or an insect's wing. Small angular or polygonal surface areas differing in color or structure from the surrounding area, forming a pattern or network; e.g., spores of many Riccia species. See areole.
areolae See areola.
areolate (L. areola: small yard, space, small area) adj. Like an areole.
areolation (L. areola: small yard, space, small area) n. The cellular network formed by the outlines of the cells of a leaf or thallus.
areole (L. areola: small yard, space, small area) n. A small, well-defined area on a surface, as the area between the veinlets of a leaf or the region of a cactus bearing the flowers and spines (or spines). A space between the threads of a net; in Cactaceae, a cluster of hairs or spines or bristles borne at the node of a leafless stem; a round or elongated often raised or depressed area on a cactus which is equivalent to a bud and from which spines, flowers, stems, or roots grow; in Mimosaceae (for example), a distinct, oblong or elliptical area on the face of a seed, bounded by a fine line. A small pit or cavity marked out upon a surface.
argenteous (L. argentum: silver) adj. Silvery.
argentous (L. argentum: silver) adj. Silvery.
argillaceous (L. argillaceus: clayish) adj. Clayey; of or pertaining to plants growing on clay soils.
argillicolous (L. argillaceus: clayish; colo, colere: to inhabit);) adj. Growing, dwelling on clay soils.
argute (L. argutus: expressive, vivid) adj. Sharp (or shrewd).
arhizous (Gr. a-: without; rizôma: roots) adj. Without roots.
arid adj. Xeric, extremely dry.
aridity n. See arid.
aril n. An outgrowth that grows around and may completely enclose the testa (seed coat) of a seed (as the red fleshy cup around a yew seed). It develops from the placenta, funicle, hilum or micropyle of an ovule. The aril surrounding the nutmeg seed forms the spice mace. See also caruncle.
arillate adj. Like an aril; possessing an aril.
arilliform adj. Aril-like.
arillode n. A false aril.
arista (L. arista: awn) n. (pl. aristae) A bristlelike structure or appendage of grain, etc.
aristae See arista.
aristate (L. arista: awn) adj. Awned; having a stiff, bristle-like awn or tip, being a projection of the midrib.
aristiform (L. arista: awn: forma: shape) adj. Awn-like.
aristolochic acid A phenanthrene-carboxylic acid derivative of a benzoisoquinoline precursors.
aristulate (L. arista: awn) adj. Bearing a small, minute awn or bristle at the tip.
armature (L. armatura: armor, arms) n. The protective covering of a plant, as thorns, spines, barbs, or prickles.
arm-cell n. Cells with incomplete septae extending inward, as in the leaf mesophyll cells of some members of the grass family.
armed adj. Bearing thorns, spines, barbs, or prickles.
aromatherapy n. The therapeutic use of plant-derived, aromatic essential oils to promote physical and psychological well-being. It is sometimes used in combination with massage and other therapeutic techniques as part of a holistic treatment approach.
aromatic adj. Having a spicy odor, at least when crushed.
aromatics n. Herbal medicines that have a pleasing odor and pungent taste.
arrangement n. A nontechnical term that refers to the way things are put together, e.g., an inflorescence may be described by the arrangement of the flowers, or leaves can be arranged opposite or alternate.
arrhenotoky (Gr. arrên, enos: male; tokos: giving birth) n. The phenomenon occurring in the reproduction of certain animals in which fertilized eggs give rise to females and unfertilized eggs to males. It is found among certain insect groups, notably the wasps and bees (Hymenoptera), and in mites, as well as rotifers and nematodes. The males are haploid and transmit only the maternal genome - their production represents arrhenotokous parthenogenesis - whereas the females are diploid. In pseudo-arrhenotoky both males and females arise from fertilized eggs and are diploid, but males subsequently become effectively haploid by inactivation of the paternal genome, either in all cells or only in germ-line cells. This occurs in certain scale insects and mites. Cf. thelytoky.
arrhythmic adj. Refers to activity which is not dependent upon light or dark. Cf. diurnal, nocturnal.
arteriosclerosis n. A chronic disease in which thickening, hardening, and loss of elasticity of the arterial walls result in impaired blood circulation. It develops with aging, and in hypertension, diabetes, hyperlipidemia, and other conditions.
arthritis n. Inflammation of a joint, usually accompanied by pain, swelling, and stiffness, and resulting from infection, trauma, degenerative changes, metabolic disturbances, or other causes. It occurs in various forms, such as bacterial arthritis, osteoarthritis, or rheumatoid arthritis.
arthroconidia See arthroconidium.
arthroconidium n. m. (pl. arthroconidia) Conidium formed from special filaments pationnned in cells in the septa.
arthrodontous adj. Having a peristome type consisting of one or two rings of triangular or linear appendages (i.e. teeth, segment), consisting essentially of differentially thickened periclinal wall-pairs (lamellae). The appendages are separated as a result of erosion or splitting of unthickened anticlinal walls, and are exposed with loss of the operculum. Transverse wall-pairs are often thickened and remain as trabeculae up the face of the teeth. Cf. haplolepidous, heterolepidous, diplolepidous, nematodontous.
arthropod n. Insect, crab, spider, centipede, or other animal from the phylum Arthropoda.
arthrospore (Gr. arthron: joint; spora: seed) n. One of a number of spores of various low fungi and algae, united in the form of a string of beads, formed by fission.
article (L. articulatus: articulation, joint) n. A segment of a jointed stem or of a fruit with constrictions between the seeds.
articulate (L. articulatus: articulation, joint) adj. Having joints; jointed; provided with places where separation may take place naturally; of a stem, having nodes; separating at maturity along a well-defined line of dehiscence.Also articulated.
articulated adj. Jointed, e.g. the more or less swollen apex of a petiolule in particular that has a line across the broadest part, with separation commonly occuring here when the leaflets fall, articulation; of a stem, having prominent nodes; of a laticifer, having cross walls. Also articulate.
articulation (L. articulatus: articulation, joint) n. A joint or point of attachment.
artifact n. A structure or appearance in a tissue due to death or the use of a reagent, and not present during life. A product of human workmanship found on archeological digs.
artificial selection The intentional human manipulation within a population to produce a desired evolutionary response. Cf. natural selection.
Artinskian n. 1. An age in the Permian Epoch, preceded by the Sakmarian, followed by the Kungurian, and dated at 268.8 to 259.7 million years ago. 2. The name of the corresponding eastern European stage, which is roughly contemporaneous with the upper Rotliegende (western Europe), lower/middle Leonardian (N. America), and the Bitaunian (New Zealand).
arundinaceous (L. arundinaceus: reed-like) adj. Reed-like in form
arylphenalenone See arylphenalenones.
arylphenalenones n. Phenalenones with aryl radicals, pigments found in Haemodoraceae, derived from 9-phenylphenalenone.
ascaricide n. An agent or substance that kills ascarids.
ascarid n. Any of various nematode worms of the family Ascaridae, which includes the common intestinal parasite Ascaris lumbricoides. They are common intestinal parasites of dogs and cats.
ascending adj. See ascending. (L. ascendere, to climb) adj. Rising or curving upward; growing erect after an oblique or semi-horizontal beginning; one that is attached above the base of the ovary and is directed upward.
asci See ascus.
ascidia See ascidium.
ascidiate adj. Pitcher-shaped, more or less tubular and often widening towards a flared mouth, especially used of the leaves of several carnivorous plants, or of carpels. Cf. conduplicate.
ascidium (Gr. askos: wineskin, bag) n. (pl. ascidia) The tubular trap formed by a pitcher (of a pitcher plant); the opening of such a trap.
ascocarp (Gr. askos: wineskin, bag; karpos: fruit) n. The reproductive body of fungi of the phylum Ascomycota, which contains ascus cells. An ascocarp may be a closed sphere (cleistothecium), a flask-shaped structure (perithecium) with a small opening (ostiole), or an open cup-shaped structure (apothecium). The ascocarp consists of both ascus-bearing and vegetative hyphae.
ascogenous adj. Ascus-producing or ascus-supporting.
ascogonia See ascogonium.
ascogonium (Gr. askos: wineskin; gonos: generation) n. (pl. ascogonia) The female sexual organ in certain ascomycetous fungi; the portion of the archicarp in certain ascomycetous fungi which receives the antheridial nuclei and puts out hyphae bearing the asci. A cell or group of cells in Ascomycotina fertilised by a sexual process.
ascohymenial adj. Of Ascomycotina having asci and paraphyses arranged as a hymenium, as in pyrenomycetes and discomycetes.
ascoma n. (pl. ascomata) An ascus-producing structure; a fruit-body containing asci.
ascomata See ascoma.
ascomycete (Gr. askos: wineskin; mykês: fungus) n. Any of a class (Ascomycetes) or subdivision (Ascomycotina) of higher fungi (as yeasts or molds) with septate hyphae and spores formed in asci. A fungus producing asci.
Ascomycetes See Ascomycota.
Ascomycota (Gr. askos: wineskin; mykês: fungus) n. A large phylum of fungi (over 30 000 species), formerly classified as a class (Ascomycetes) or a subdivision (Ascomycotina). It includes the yeasts, some species of edible fungi (truffles), Penicillium, Aspergillus and Claviceps purpurea, which causes ergot in rye. Many are fungal partners of lichens. These fungi are known as the sac fungi because their spores are formed in a saclike structure (called an ascus). Sexual reproduction is by means of ascospores produced within the ascus. The asci are usually grouped together in an ascocarp. Syn. Ascomycotina, Ascomycetes.
Ascomycotina See Ascomycota.
ascospore (Gr. askos: wineskin; spora: seed) n. Any of the spores contained in an ascus.
ascosporic See ascospore.
ascus (Gr. askos: wineskin, bag) n. (pl. asci) A specialized cell in fungi of the phylum Ascomycota, which contains two haploid nuclei that fuse during sexual reproduction and then undergo meiosis, giving rise to eight ascospores contained within the ascus.
ascyphous adj. Without a cup - especially in Cladonia.
asepalous adj. Without sepals.
aseptate adj. With no partitions or divisions.
asexual adj. Not forming part of a cycle which involves fertilisation and meiosis. Lacking sexual characteristics as in a sterile ray floret; or when referring to reproduction, occurring without the fusion of egg and sperm.
asexual propagation The propagation of plants through means other than fertilization, including layering, cuttings, tissue cultures and the division of clumps.
asexual reproduction Not involving, or requiring, fertilization and meiosis. Reproduction in which new individuals are produced from a single parent without the formation of gametes. It occurs chiefly in lower animals, microorganisms, and plants. In microorganisms and lower animals the chief methods are fission (e.g. in protoctists), fragmentation (e.g. in some aquatic annelid worms), and budding (e.g. in cnidarians and yeasts). The principal methods of asexual reproduction in plants are by vegetative propagation (e.g. bulbs, corms, tubers) and by the formation of spores. Spore formation occurs in mosses, ferns, and other plants showing alternation of generations, as a dormant stage between sporophyte and gametophyte, and in some algae and fungi, to produce replicas of the organism. Cf. sexual reproduction.
aspect n. The appearance of vegetation during one of the seasons of the year, e.g., the vernal aspect. The direction toward which a slope is facing, e.g., the southern aspect.
aspection n. The change in the appearance of vegetation and its visible attributes during the succession of seasons of the year, as budding in prevernal, flowers in vernal, green fruit in estival, ripe fruit in serotinal, and bare branches in hibernal.
Aspergillus A genus of fungi that includes many moulds found in rotting food. A. fumigatus can cause disease in humans (called aspergillosis), while A. flavus can infect peanuts, producing the poison aflatoxin, which can cause cancer.
asperity (L. asperitas: (rough) bump) n. A tiny projection or hairlike prickle of an epidermal cell.
asperous (L. asper: rough) adj. Rough to the touch.
asperulate (L. asper: rough) adj. Slightly rough to the touch.
asperulous (diminutive of L. asper: rough) adj. Refers to a surface with short, hard projections; slightly roughened.
asphodelin n. A yellow colored anthraquinone.
aspirin n. A drug that reduces inflammation, combats fever, and alleviates pain. Aspirin works by inhibiting the formation of prostaglandins, which are major factors in the inflammation process. It also reduces the aggregation of blood platelets, hence its use in maintaining blood flow following heart and circulatory disorders. Syn. acetylsalicylic acid.
Aspleniaceae n. A family of the phylum Filicinophyta.
Asplenium n. A genus of the family Aspleniaceae.
Asselian n. 1. An age in the Early Permian Epoch, preceded by the Stephanian, Gzelian, and Noginskian (Carboniferous), followed by the Sakmarian, and with an initial boundary (the Carbo-Permian boundary) dated at 290 million years ago. 2. The name of the corresponding eastern European stage which, because of lower boundary uncertainties, has also been considered as part of the Carboniferous system. It is roughly contemporaneous with the lower Wolfcampian and lower Rotliegende (western Europe), and with the lower Somoholoan (New Zealand). See also Sakmarian.
assimilation Cellular conversion of raw materials into structures useful to a plant, such as cell walls and protoplasm.
association complex A group of associations which occurs in a defined area.
association fragment A stand of plants that requires other characteristics to meet community standards.
association segregate A climax community which has changed from the original community, like a mature beech-maple association appearing from a mixed deciduous forest.
association table A list of species that occurs in several stands of an association or community, including data on characteristics such as abundance, cover, vitality, etc. Syn. synthesis table, stand table.
associes n. A temporary community in developmental stage.
assumenta See assumentum.
assumentum n. (pl. assumenta) A valve of a silique.
assurgent (L. assurgere: to rise, to get up) adl. Curving upwards. See ascending.
astemonous (Gr. a-: without; stêmôn: thread) adj. Without stamens.
asterean adj. Belonging to or similar to plants of the aster family, Asteraceae (Compositae). (Gr. a-: without; stoma, stomatos: mouth) adj. Having no mouth, stoma, or stomata; of an indehiscent capsule. Cf. cleistocarpous. Also astomous.
asthma n. A chronic respiratory disease, often arising from allergies, that is characterized by sudden recurring attacks of labored breathing, chest constriction, and coughing.
astomous (Gr. a-: without; stoma: mouth) adj. In mosses, refers to a capsule without a mouth. Used of capsules which have no regularly dehiscent lid or operculum. Also astomatous.
astragaloid adj. Cubical.
astringency n. See astringent.
astringent (L. adstringere: to tighten) (prefix ad-, with the sense of reduction and L. stringere, bind) adj. n. Constricting or contracting; an astringent substance or drug. A substance or preparation, such as alum, that draws together or constricts body tissues and is effective in stopping the flow of blood or other secretions.
astrosclereid n. A sclereid cell with rather short, stout branches. Cf. brachysclereid, macrosclereid, trichosclereid.
astylocarpellous (Gr. a-: without; stylos: column; karpos: fruit) adj. Lacking a style and a stipe.
astylocarpepodic (Gr. a-: without; stylos: column; karpos: fruit; pous, podos: foot) adj. Without a style, but with a stipe.
astylous (Gr. a-: without; stylos: column) adj. Without a style.
asymmetric adj. Not divisible into equal halves, as in some leaves; irregular in shape; having a different shape on each side of a central axis. Also asymmetrical.
asymmetrical See asymmetric.
asymptotic population The maximum size possible to a population under present conditions, no matter how long reproduction is allowed to continue.
asynapsis n. The failure of pairing of homologous chromosomes during meiosis.
atactostele n. A variant of a stele in which the vascular bundles are sctterd through the ground tissue. Cf. eustele, dictyostele, protostele, siphonostele.
atavistic adj. Reverting to a form found in ancient ancestors.
ataxonomic adj. An approach in which interpretations are not based on taxonomic assignment; for example: if a fossil taxon has the same generic name as an extant taxon, interpretations about the ecology of the fossil taxon are not based on the ecology of the extant taxon.
atelechory (Gr. a-: without; têlë: far, distant; khôreô: to move) n. Inhibited seed dispersal. A number of plants have evolved mechanism which inhibits dispersal. For example, there may be few sites in a desert which provide a plant with sufficient moisture to grow. If a desert annual has succeeded in surviving and reproducing at a particular location, is is likely that growth should be possible the next season too. In is then the plant interest to have its seeds remain where they were produced. Examples include basicarpy (fruit produced at the base of the plant) and geocarpy (fruits carried on long peduncles into the soil, e.g. Trifolium subterraneum).
athecal (Gr. a-:without; thêkê: box, case) adj. Without a sheath of tissue.
atheroma See atherosclerosis.
atherosclerosis n. Patchy thickening of the lining of arteries caused by the deposition of fatty material and fibrous tissue. This tends to obstruct the blood flow and predisposes to thrombosis, which may lead to a heart attack or a stroke. In the Western world atherosclerosis is common in adults: its cause is believed to be associated with a diet high in animal fats (see cholesterol) and refined sugar, cigarette smoking, and obesity. Its incidence increases with age and it is exacerbated by high blood pressure. Its extent can be reduced by treatment of any underlying illness. Syn. atheroma.
Atokan n. A series in the Pennsylvanian of N. America, underlain by the Morrowan and overlain by the Desmoinesian Series. It is roughly contemporaneous with the Vereiskian and Kashirskian Stages of the Moscovian Series.
atoll n. A circular coral island or islands surrounding a body of water in the ocean. Cf. lagoon.
atomate adj. Bearing sessile or subsessile glands.
atomiferous See atomate.
ATP 'adenosine triphosphate'. A relatively stable, high energy molecule used to fuel chemical reactions within cells. See adenosine triphosphate.
atratous (L. ater, tra, trum: black) adj. Blackened or turning black, as the stems and leaves of Papillaria,
atro- (L. ater, tra, trum: black) prefix. Dark or blackish.
atrocastaneous adj. Very dark chestnut in color.
atrophy n. A wasting away from lack of nutrition or use. Arrested development of a part or organ inconsequential to the normal development of a plant or animal.
atropous adj. An erect, straight ovule with funicle, chalaza and micropyle in a straight line, Cf. amphitropous, anatropous, campylotropous, circinotropous, hemitropous.
atropous ovule See orthotropous ovule.
atropurpurea (L. ater, tra, trum: black; purpura: the purple color) adj. Dark, deep purple, often almost blackish. Also atropurpureus.
atropurpureus See atropurpurea.
attenuate (L. ad: towards; tenuitas: fineness, sharpness) adj. Gradually narrowed to a long point at apex or base, tapering gradually, as at the base or tip of a leaf or flower parts, drawn out into a long point. See also acute.
atypical adj. Not normal.
auctoris Used in taxonomy when an author has applied a wrong name, usually beginning with 'non', to contrast it to the true type with the correct author, e.g., Betula platyphylla auct. Non Sukachev, which is in fact a different plant, Betula mandschurica; (abbreviated auct., auctt.). Also auctorum.
auctorum See auctoris.
aucubin n. A bitter-tasting route II decarboxylated iridoid.
aureol n. a phytoalexin.
auricle (L. auricula; ear, ear-lob) n. Any ear-like lobed appendages, at the base of a leaf, leaflet or corolla lobe, often present at the basal margins of leaf in mosse and on thalli and other organs in liverwort.
auriculate (L. auricula; ear, ear-lob) adj. Having an auricle; with the leaf base composed of two rounded lobes. Syn. eared.
auriculate-clasping (L. auricula; ear, ear-lob) adj. With earlike lobes at the base of a leaf, encircling the stem.
auriculiform (L. auricula; ear, ear-lob; forma: shape) adj. Having the shape of an ear.
aurieles n. Small lobes at the basal angles of the leaf, usually consisting of cells differing in size, shape, or both from those of the main part of the leaf. Properly used only when there is an outward curve in the outline of the leaf at the base, but often used loosely to denote the basal angles of widely decurrent leaves.
aurone See aurones.
aurones n. golden-colored flavonoids with Z-sterochemistry at the double bond, often found in flowers.
austral (L. australis: southern) adj. Southern; of the Southern Hemisphere.
autapomorphic adj. Describes a derived characteristic unique to a given taxon or monophyletic group. See also: apomorphic, synapomorphic.
autapomorphy n. A derived trait or apomorphy that is unique to only one group. See apomorphy.
autecism See autoecism.
autecology The study of the individual in relation to environmental conditions, or sometimes, members of a species studied collectively in the same way.
author n. The botanist who discovered and named the new species. The name or initial(s) following the binomial, designating that botanist.
autocarp (Gr. autos: self; karpos: fruit) n. A fruit produced through self-fertilization.
autochore n. A species in which some action of the parent plant is the chief force for dissemination, e.g., the mechanical projection of seeds in jewelweed, Impatiens.
autochory (Gr. autos: self; khôreô: to move) n. The dispersal of plant seeds by the plants themselves, via expulsion mechanisms, etc., e.g. some fruits explode or shoot their seeds, e.g. Viola, Oxalis, Geranium, Impatiens, etc.
autochthonous (Gr. autos: self; khthon: earth, country) adj. Of the inhabitants of a region, original; earliest known; (applied to an element of the Australian flora rich in endemics and believed to have been evolving in Australia for a long period of time). Materials, especially rock masses, that formed in their present location and have not been transported. Fault surfaces can separate indigenous rocks from allochthonous rocks, although some allochthonous rocks are clearly delineated by their differing composition.
autochtonous See autochthonous.
autocious See autoecious.
autodiploidization n. Self-inducing fusion of nuclei.
autoecious (Gr. autos: self; oikos: house) adj. Refers to parasites which pass all stages of their life cycle on or within the same host, like certain rust fungus. Having male and female organs on the same plant. Also autocious. Cf. heteroecious.
autoecism (Gr. autos: self; oikos: house) n. The development fo the entire life cycle of a parasitic fungus on a single host or group of hosts. Syn. autecism.
autogamic See autogamous.
autogamous (Gr. autos: self; gamos: marriage) adj. Relating to, or reproducing by autogamy; self-fertilized. Syn. autogamic.
autogamy (Gr. autos: self, gamos: marriage) n. Self-fertilization, pollination of a flower by its own pollen. Opposed to allogamy.
autogenic succession Vegetational progression in which each stage modifies the habitat in such a way that it is replaced by another stage, e.g., pond shoreline herbaceous plants being replaced by shrubs.
autoicous (Gr. autos: self; oikos: house) adj. Having antheridia and archegonia in separate clusters on the same plant. Cf. cladautoicous, gonioautoicous, pseudautoicous, rhizautoicous, synoicous, paroicous, dioicous, monoicous.
autolysis n. The digestion of an organism or parts of it by its own enzymes.
autonomic adj. Refers to processes or activities that are spontaneous, arising from internal causes. Also autonomous.
autonomous adj. Autonomic. Refers to plants, especially those with chlorophyll, that are capable of turning inorganic materials to organic ones for their nutrition or other use. Cf. autotrophic, photosynthesis.
autonym n. When an author names a new subspecies or variety, the species is given the same new rank, based on the original type of the species and duplicating the epithet, e.g., when Pinus nigra ssp. larico was designated, Pinus nigra ssp. nigra came into being.
autophilous (Gr. autos: self; phyllon: leaf) adj. Self-pollinated
autophytic (Gr. autos: self; phyton: plant) Any plant which produces its own food. See autotrophic.
autoploid (Gr. autos: self; eidos: form) adj., n. An individual with chromosome sets characteristic of the species.
autopolyploid (Gr. autos: self; polys: many; eidos: form) adj., n. A polyploid organism in which the multiple sets of chromosomes are all derived from the same species. For example, doubling of the chromosome number during mitotic cell division, possibly induced by colchicine, gives rise to a tetraploid known as an autotetraploid. A polyploid that arises by the multiplication of the complete haploid genome of a single species. Cf. allopolyploid.
autotroph See autotrophe.
autotrophe (Gr. autos: self; trophê: food) n. An organism which uses light energy to synthesize sugars and proteins from inorganic substances. Green plants are by far the most common autotrophes. Certain bacterias and protozoans are also autotrophic.
autotrophic (Gr. autos: self; trophê: food) adj. Independent of other organisms in respect of organic nutrition; i.e. capable of utilizing only inorganic materials as a source of food, as most plants and certain bacterias and protozoans; able to fix carbon dioxide, by photosynthesis, to form carbohydrates. Producing its own nutritive substances; containing chlorophyll and, therefore, green; photosynthetic. Lakes in which most of the organic matter is from autochthonous sources are referred to as 'autotrophic', whereas those dominated by the input of paralimnetic particulate organic matter (POM) and dissolved organic matter (DOM) are termed 'allotrophic'. See autotrophe.
autotrophic nutrition A type of nutrition in which organisms synthesize the organic materials they require from inorganic sources. Chief sources of carbon and nitrogen are carbon dioxide and nitrates, respectively. All green plants are autotrophic and use light as a source of energy for the synthesis, i.e. they are photoautotrophic (see photosynthesis). Some bacteria are also photoautotrophic; others are chemoautotrophic, using energy derived from chemical processes (see chemosynthesis). Cf. heterotrophic nutrition.
autumnal adj. Flowering or appearing in the autumn.
auximone (Gr. auximos: promoting growth) n. A class of substances essential in minute amounts to stimulate growth,
auxin (Gr. auxanô: to grow) n. Any of a group of plant growth substances responsible for such processes as the promotion of growth by cell enlargement, the maintenance of apical dominance, and the initiation of root formation in cuttings. Auxins are also involved in the abscission of leaves, fruit, or other plant organs and in the development of flowers and fruits. Naturally occurring auxins, principally indoleacetic acid (IAA), are synthesized in actively growing regions of the plant, from where they are transported to other parts of the plant. Synthetic auxins include 2,4-D, which is used as a weedkiller, and indolebutyric acid and naphthaleneacetic acid, which are sold in preparations of 'rooting hormones'.
auxospore n. A cell that restores the original size to the diminishing products of cell division.
auxotelic adj. Describes an inflorescences, parts of inflorescences or axes that do not end in a flower, and in which growth continues beyond the flowering region, Cf. anauxotelic.
available nutrient The portion of nutrient substances, such as nitrates in the soil, that can be utilized by plants at rates and amounts required for growth.
available water That portion of water held in soil that may be absorbed into the roots of the plant.
available water-holding capacity The amount of water in soil that can be absorbed by plants, between the high amount at full saturation or field capacity, and the low amount at the permanent wilting capacity.
average distance The mathematical statement of the distance between plants calculated by dividing the square root of an area by the density of each species within the area.
averse (L. aversus: turned away) adj. Turned away form the central axis; Opposed to adverse.
awl n. A pointed tool for marking surfaces or piercing small holes (as in leather or wood).
awl-shaped adj. Tapering upward from the base to a slender or rigid point. Short, narrowly triangular, and sharply pointed like an awn.
awn n. A stiff, bristlelike appendage, usually at the end of a structure, e.g. on the tip or back of the lemma of a grass floret or formed by an excurrent costa.
awned adj. Possessing an awn.
axes See axis.
axe-shaped adj. Dolabriform; describes three-dimensional shapes.
axial (axis: axle) adj. Of, pertaining to, characterized by, or forming an axis; situated in an axis or on the axis. See axile.
axial parenchyma Axially orientated xylem parenchyma in the wood. See aliform, apotracheal, banded and paratracheal. Cf. ray parenchyma.
axial strand See central strand.
axil (L. axilla: armpit) n. The angle found between any two organs or structures. The angle between a branch or leaf and the stem it grows from. Axillary (or lateral) buds develop in the axil of a leaf. The presence of axillary buds distinguishes a leaf from a leaflet.
axile adj. Situated along the central axis of an ovary having two or more locules.
axile placentation Ovules attached to the central axis of an ovary with two or more locules.
axilla n. (pl. axillae) An axil.
axillae See axilla.
axillary (L. axilla: armpit) adj. Positioned in or arising in an axil, growing in an axil, as buds.
axillary bristle A long, rigid, awn-like axillary structure, appearing to originate from the leaf axil but standing clear of the leaves, as in Hypopterygium commutatum.
axillary bud See axil.
axillary hair Uniseriate hair found in the leaf axils, generally inconspicuous and well concealed by the leaf bases. The apical and basal cells of the hairs are frequently differentiated in size or color. Cf. axillary bristles.
axillary hyaline nodule A cluster of inflated, hyaline cells in leaf axils of Fissidens representing a potential branch primordium.
axis (L. axis: axle) n. (pl. axes) A stem; commonly used for the main stem of a whole plant or of an inflorescence. The longitudinal, central supporting structure or line around which various organs are borne, as a stem bearing leaves.
azetidine-2-carboxylic acid n. A non-protein amino acid, an alpha-amino acid with a primary -imino group (-NH) and a carboxyl group attached to the same carbon atom.
Azoic See Archaean.
Azollaceae n. A family of the phylum Filicinophyta.
azonal adj. Refers to soil that has no well developed profile with horizons, such as glacial deposits, dune sand, alluvium.
azonate adj. Without zones, without concentric markings.