machaerantheroid (Gr. makhaira: knife; anthos: flower; eidô: to look like) adj. Having involucral bracts with recurved tips.

macro- (Gr. makros: long) prefix. Meaning long, large, great

macrocarpous (Gr. makros: large; karpos: fruit) adj. Having large fruits.

macrocladous (Gr. makros: long; klados: klados: branch) adj. With long branches.

macroconidia See macroconidium,

macroconidium n. (pl. macroconidia) Large leaf or club-shaped asexual extracellular spores produced from vegetative hyphae.

macrocyst (Gr. makros: large; kystis: swollen sac, bladder) n. A large cyst, or spore case, especially the encysted, resting plamodium of a slime mold.

macroevolution (Gr. makros: large; L. evolutio: unfolding, unrolling) n. Evolution above the species level, i.e. the development of new species, genera, families, orders, etc. There is no agreement as to whether macroevolution results from the accumulation of small changes due to microevolution, or whether macroevolution is uncoupled from microevolution.

macronema n. (pl. macronemata) Large, branched, rhizoids produced around branch primordia and at the base of buds. Cf. micronema.

macronemata See macronema.

macrophanerophyte (Gr. makros: long; phaneros: visible, manifest; phyton: plant) n. A phanerophyte of size between 24 and 50 meters (73 and 152 feet).

macrophyll (Gr. makros: large; phyllon, leaf) n. The relatively large, expanded leaf of higher vascular plants. Cf. megaphyll, microphyll.

macrophyllous (Gr. makros: large; phyllon: leaf) adj. With large leaves or leaflets; with macrophylls.

macrophyte (Gr. makros: large; phyton: plant) n. A member of the macroscopic plant life especially of a body of water; large aquatic plant; the term 'aquatic macrophyte' has no taxonomic significance.

macropodial adj. Said of an embryo in which the reserves are stored in the hypocotyl.

macropodous (Gr. makros: long; pous, podos: foot) adj. Of a leaf, having a long stalk.

macrosclereid n. A sclereid cell circa 2X longer than broad, lacking processes.

macroscopic (Gr. makros: large; skopeô: to aim, watch, examine) adj. Items large enough to be observed by the naked eye.

macrosporangia See macrosporangium.

macrosporangium (Gr. makros: large; spora: seed; aggeion: vase, bowl, container) n. (pl. macrosporangia) The receptacle in which macrospores are developed. Syn. megasporangium.

macrospore (Gr. makros: large; spora: seed) n. One of the specially large spores of certain flowerless plants, as Selaginella, etc. Syn. megaspore.

macrosporophyll (Gr. makros, long; phyllon, leaf) A leaflike structure that bears macrosporangia. See megasporophyll.

macrostylous (Gr. makros: long; stylos: column, pilar) adj. With a long style. Cf. microstylous, mseostylous.

macula (L. macula: spot, mark, blotch) n. (pl. maculae). A spot or blotch.

maculae See macula.

maculate (L. maculatus: spotted, marked, blotched) adj. Spotted or blotched.

maesaquinone n. A benzoquinone.

magnoliid n. Any member of the basal assemblage of flowering plants.

Magnoliophyta n. Division of the plant kingdom consisting of those organisms commonly called the flowering plants, or angiosperms. The angiosperms have leaves, stems, and roots, and vascular, or conducting, tissue (xylem and phloem). The ovules, which develop into seeds, are enclosed within an ovary, hence the term angiosperm, meaning enclosed seed. The flowering plants are the source of all agricultural crops, cereal grains and grasses, garden and roadside weeds, familiar broad-leaved shrubs and trees, and most ornamentals.

Magnoliopsida n. A phylum within the plant kingdom comprising plants with a vascular system that bear flowers during at least some stage of their life cycle. The phylum is further subdivided into dicotyledons and monocotyledons. The Magnoliopsida is the largest phylum of land plants, represented by over 250 000 species world-wide. Syn. Angiospermophyta.

malacophyllous (Gr. malakos: soft; phyllon: leaf) adj. With soft leaves

male cone The conical, pollen-bearing male element of a conifer.

malegametophyte n. A plant body or cell lineage formed by vegetative growth of the microspore.

malignant adj. Threatening to life; virulent: a malignant disease. Tending to metastasize; cancerous.

mallee n. A growth habit in which several woody stems arise separately from a lignotuber (usually applied to shrubby eucalypts); a plant having the above growth habit.

malodorous (L. malus: bad; odor: smell) adj. Having a disagreeable, unplesant odor; smelling bad.

malpighiaceous hair See malpighian hair.

Malpighian layer A palisade layer of the seed, esp. of the exotesta, that has much thickened walls.

malpighian hair Straight hairs tapering to both free ends and attached near the middle; pick-shaped; a unicellular, T-shaped hair with a short stalk and often looking fusiform from above. Also malpighiaceous hair. Syn. dolabriform.

malvaceous (L. malva: mallow) adj. Mallow-like. Belonging to the Malvaceae, or mallow family, comprising the abutilon, okra, cotton plant, etc.

malvoid adj. Said of a leaf tooth in which the medial vein forms a non-glandular persistent apex, lateral veins are not involved.

mammiform (L. mamma: breast, teat; forma: shape) adj. Breast-shaped.

mammilate See mammillate.

mammilla (L. mamilla: breast, teat) n. (pl. mammillae) A nipple-like protuberance; a strongly bulging surface of a cell; also used for various hollow papilla-like protuberences without associated local wall thickening.

mammillae See mammilla.

mammillary (L. mamilla: breast, teat) adj. Of, pertaining to, or ressembling a mammilla.

mammillate (L. mamilla: breast, teat) adj. Having small nipple-shaped projections; with nipple-like protuberances; convex to hemispherical with a blunt central projection; e.g. the operculum of Bryum. Syn. mammillated. Also mammillose, mammilate.

mammillated See mammillate.

mammillation n. See mammillate.

mammillose adj. With mamillae.

mange n. Any of several chronic skin diseases of mammals caused by parasitic mites and characterized by skin lesions, itching, and loss of hair. Also scabies

mangiferin n. A xanthone.

mangostin n. A xanthone.

mangrove n. Any of certain shrubs and trees of the families Rhizophoraceae, Verbenaceae, Sonneratiaceae, and Arecaceae that grow in dense thickets or forests along tidal estuaries, in salt marshes, and on muddy coasts. The term also applies to the thickets and forests of such plants. Mangroves characteristically have prop roots (exposed, supporting roots). In addition, in many species respiratory, or knee, roots project above the mud and have small openings through which air enters, passing through the soft, spongy tissue to the roots beneath the mud. Mangrove fruits put out an embryonic root before they fall from the tree; the root may fix itself in the mud before the fruit separates from the parent. Likewise, branches and trunks put out adventitious roots which, once they are secure in the mud, send up new shoots. The common mangrove (Rhizophora mangle) grows to about 30 ft (9 m) tall and bears short, thick, leathery leaves on short stems, and pale-yellow flowers. Its fruit is sweet and wholesome.

mangrove swamp A region of vegetation, found along tropical coasts, in which mangrove trees (Rhizophora species) predominate. The waterlogged soil is highly saline, and - like other halophytes - mangroves are adapted to withstand these conditions; they also possess aerial roots (pneumatophores) through which gaseous exchange occurs, to counteract effects of the badly aerated soil.

manicate adj. Wwith a thick, interwoven pubescence.

mannitol n. A hexitol formed by reduction of mannose or fructose; it occurs in gum exudates.

mannose n. A hexose sugar, an isomer of sucrose.

mannoxylic See manoxylic.

manoxylic (Gr. manos: rare; xylon: wood) adj. Of wood in which there is a great deal of parenchyma tissue among the xylem, i.e. there is little xylem and plenty of parenchyma. Cycads and pteridosperms have mannoxylic wood. Contrast with pycnoxylic.

marcescent (L. marcescere: to wither, to wilt) adj. Withering but remaining persistent, without falling off, as the sepals and petals in some flowers or the leaves at the base of some plants, as the leaves of Bartramia subulata.

margin (L. margo, marginis: edge) n. An edge of a flat structure, such as a leaf.

marginal (L. margo, marginis: edge) adj. Occurring at or very close to the margin, frond or other lobe; pertaining to the margin, especially as applied to a leaf.

marginal placentation Ovules attached to the juxtaposed margins of a simple pistil.

marginate (L. marginare: to border) adj. With a border of a different color; with a distinct margin.

margined (L. margo, marginis: edge) adj, With margins.

margo n. The peripheral part of the membrane in a bordered pit in gymnosperms, etc., consisting of rather sparse cellulose maicrofibrils.

marsh n. A tract of wet land principally inhabitated by emergent herbaceous vegetation.

Marsileaceae n. A family of the phylum Filicinophyta.

marsupia See marsupium.

marsupium n. (pl. marsupia) A modified shoot calyptra; associated with the development of a sporophyte in a pouch-like structure that penetrates downward into the substrate (geocauly); e.g., Goebelobryum. Cf. coelocaule.

massula n. (pl. massulae) A general term for aggregations of pollen grains dispersed as a unit, e.g in the Mimosaceae, Periplocaceae; a group of microspores enclosed in a hardened mucilage.

massulae See massula.

massule n. A large mass of mucilagenous material that encloses the microspores of water ferns like Azolla.

mastitis n. Inflammation of the breast.

matinal adj. Blooming in the early morning.

matroclinal adj. Of a plant that exhibits certain characters inherited from the female parent as in certain banana (Musa) hybrids, which more nearly resemble the female parent rather than having intermediate characters.

mature adj. A later phase of growth characterized by flowering, fruiting, and a reduced rate of size increase.

mauve adj. Bluish or pinkish-purple.

mazaedia See mazaedium.

mazaedium n. (pl. mazaedia) A spore mass formed in fruits of Caliciales in which spores, generally with sterile elements, become free from the ascus as a dry, loose, often dark, powdery mass on the fruiting surface.

mealy adj. powdery, farinaceous.

medifixed (L. medium: middle; fixus: fixed, fastened) adj. Attached by or at the middle, e.g. of anthers, attached to the filament at the middle of the connective.

medulla (L. medulla: marrow, innermost part) n. (pl. medullae) The central tissue of a structure, generally referring to the pith. Used in liverworts to denote the internal stem and seta tissue when the term cortex is used for the epidermis. The inner part of the thallus of a lichen.

medullae See medulla.

medullary (L. medulla: marrow, innermost part) adj. Made up of pith, spongy; pertaining to, consisting of, or ressembling the medulla.

medullated adj. With pith, used e.g. when talking about stelar morphology.

mega- (Gr. megas: big, strong) prefix. Meaning large, great, vast, powerful.

megagametophyte (Gr. megas: big, strong; gametęs: spouse; phyton: plant) n. A plant body or cell lineage, formed by vegetative growth of the megaspore, that produces the female gametes of a heterosporous plant.

megaphanerophyte (Gr. megas: big, strong; phaneros: visible, manifest; phyton: plant) n. A phanerophyte of size above 50 meters (152 feet).

megaphyll (Gr. megas: big, strong; phyllon: leaf) n. A type of foliage leaf in ferns and seed plants that has branched or parallel vascular bundles running through the lamina. The megaphylls of ferns are large pinnate leaves called fronds. A megaphyll was formerly called a macrophyll. Cf. microphyll.

megaphyllous (Gr. megas: big, strong; phyllon: leaf) adj. With large leaves.

megasporangia See megasporangium.

megasporangium (Gr. megas: big, strong; spora: seed; aggeion: vase, bowl, container) n. (pl. megasporangia) A spore-producing structure (sporangium) which bears megaspores. The larger of the two kinds of sporangia produced in the sexual life cycle of a heterosporous plant.

megaspore (Gr. megas: big, strong; sporos, seed) n. The larger of the two kinds of spores produced in the sexual life cycle of a heterosporous plant, giving rise to the female gametophyte; the megaspore is a haploid that develops from megaspore mother cell into the female gametophyte; the spore is usually not shed but remains on the parent plant and develops in situ. Syn. gynospore.

megaspore mother cell A diploid cell in plants that divides by meiosis to give rise to four haploid megaspores (see sporophyll). In flowering plants the megaspore mother cell (or embryo mother cell) is situated in the ovule. One of the megaspores it produces develops into the embryo sac; the others abort.

megasporocyte (Gr. megas: big; sporos: seed; kytos: what covers) n. A cell that undergoes meiosis to produce four megaspores. See megaspore mother cell.

megasporophyll (Gr. megas: big; sporos: seed; phyllon: leaf) n. A specialised leaf upon (or in the axil of) which one or more megasporangia are borne. See sporophyll.

meiosis (Gr. meioô: to reduce) n. The two-stage division of a diploid nucleus, occurring once in every sexual life cycle, in which gene recombination occurs and the number of chromosomes characteristic of the sporophyte plant is halved prior to the production of gametes. Two consecutive divisions occur. In the first, homologous chromosomes become paired and may exchange genetic material (see crossing over) before moving away from each other into separate daughter nuclei. This is the actual reduction division because each of the two nuclei so formed contains only half of the original chromosomes. The daughter nuclei then divide by mitosis and four haploid cells are produced. See also prophase; metaphase; anaphase; telophase. Syn. miosis.

meiospore. n. A spore produced in the meiosis.

meiotic adj. Pertaining to meiosis: a two stage type of cell division in sexually reproducing organisms that produces gametes with half the chromosome number of the original cell.

melanin n. A class of compounds found in plants, animals, and protists, where it serves predominantly as a pigment. In humans, melanin is the primary determinant of human skin color. Melanins have very diverse roles and functions in various organisms. A form of melanin makes up the ink used by many cephalopods as a defence mechanism against predators. Melanins also protect microorganisms, such as bacteria and fungi, against stresses that involve cell damage by solar UV radiation or generation of reactive oxygen species. In many pathogenic microbes melanins appear to play important roles in virulence and pathogenicity by protecting the microbe against immune responses of its host.

melanize v. To convert into, or infiltrate with melanin. To make or become black.

melanization n. See melanize.

melanocyte n. Melanin-forming cell. Also melanodendrocyte.

melanodendrocyte See melanocyte.

melanophyllous (Gr. melas, melanos: black; phyllon, leaf) adj. With dark leaves.

melanoxylon (Gr. melas, melanos: black; xylon: wood) n. Dark wood.

mellitophily (L. mellitus: of honey; philos: friend) n. Pollination by bees.

meloniform (L. melo, melonis: melon; forma: shape) adj. Melon-shaped; irregularly spherical with projecting ribs.

membranaceous (L. membranaceus: made up of a membrane) adj. Like a membrane; thin, rather soft, and more or less translucent. Syn. membranous.

membranous (L. membrana: membrane) See membranaceous.

menarche n. The first menstrual period, usually occurring during puberty.

meniscoid (Gr. męniskos: crescent; eidô: to look like) adj. Concavo-convex; one side concave and the other convex; resembling a watch-glass. Also meniscoidal.

meniscoidal See meniscoid.

mentum (L. mentum: chin) n. A projection formed by the extension of the base of the column in some orchids.

mephitic (L. mephiticus: mephitic) adj. Having a strong, disagreeable odor.

Meramecian (L. mentum: chin) n. A series in the Mississippian of N. America, underlain by the Osagean, overlain by the Chesterian, and roughly contemporaneous with the Arundian, Holkerian, and Asbian Stages of the Visean Series of Europe

mericarp (Gr. meros: part; karpos: fruit) n. One segment of a fruit that breaks at maturity into units derived from the individual carpels. Cf. schizocarp. Syn. hemicarp. One of the two carpels that resembles achenes and forms the schizocarp of an umbelliferous plant.

mericlinal adj. Of a periclinal form in which the outer layers of tissue occupy only a sector rather than completely enclosing the inner layer.

Merionsian n. A stage in the Lower Devonian of Australia, underlain by the Crudinian, overlain by the Cunninghamian, and roughly contemporaneous with the Siegenian of Europe.

meristem (Gr. meristęs: dividing) n. The growing regions of a plan, made of a plant tissue consisting of actively dividing cells that give rise to cells that differentiate into new tissues of the plant, to produce the definitive tissues and organs. The most important meristems are those occurring at the tip of the shoot and root (see apical meristem) and the lateral meristems in the older parts of the plant (see cambium, cork cambium).

meristematic (Gr. meristęs: dividing) adj. Of or pertaining to the meristem.

meristemoid n. A dividing cell, or small group of dividing cells, surrounded by more or less differentiated and undividing cells, e.g. a stomatal meristemoid, a cell whose immediate derivatives produce the stomata and sometimes subsidiary cells.

merogony n. An individual with the egg cytoplasm from one parent and the egg nucleus from the other parent.

merophyte (Gr. meros: part; phyton: plant) n. Part of a plant; applied to a segment cut or divided from the apical cell and all tissues and organs derived from it by subsequent division; e.g., a segment or initial merophyte that forms leaf, epidermal and cortex initials will form a mature merophyte consisting of one leaf and associated stem tissue; a plant is composed of innumerable merophytes. Cf. merophytes.

merophytes (Gr. meros: part; phyton: plant) n. Group of cells which have all been produced from the same initial cell. Leaves and stems in particular are often built from specific patterns of merophytes.

merous (Gr. meros: part) used as a suffix. Meaning parts of a set. A 5-merous corolla would have five petals. Of the number of parts per whorl that characterises a particular flower, e.g. 3-merous.

mery n. The number of parts per whorl that characterises a particular flower (generally constant for the perianth whorls and less often for the whorl(s) of stamens also).

mesarch (Gr. mesos: in the middle; arkhę: origin) adj. Having the metaxylem develop on both sides of the protoxylem.

mescaline n. A protoalkaloid.

mesic (Gr. mesos: in the middle) adj. Conditioned by temperate moist climate; pertaining to conditions of medium moisture supply, i.e. applied to an environment that is neither extremely wet (hydric) nor extremely dry (xeric).

mesifixed adj. Attached by or at the middle, e.g. of anthers.

meso- (Gr. mesos: in the middle) prefix. Meaning middle, in the middle.

mesocarp (Gr. mesos: in the middle; karpos: fruit) n. The fleshy portion of the wall of a succulent fruit inside the skin and outside the stony layer, if any, surrounding the seed(s). Cf. endocarp and exocarp.

mesochile n. The intermediate or middle part of the lip of orchids when this structure is separated into three distinct parts, as in Stanhopea.

mesocotyl n. The internode between the cotyledon and the coleoptile in a grass embryo or seedling, also, an internode developing between the unequal cotyledons in some Gesneriaceae-Cyrtandroideae and -Epithematoideae after germination.

mesogamy n. Fertilisation during which the pollen tube penetrates the ovule laterally by way of the integuments.

mesogenous adj. Said of stomatal ontogeny in which the subsidiary cells are produced from the same cell (meristemoid, initial) that gives rise to the guard cell initials.

mesohyalocysts See parateniola.

mesohydric adj. Being intermediate between endohydric and exohydric.

mesoperigenous adj. Said of stomatal ontogeny in which at least one of the subsidiary cells is produced from the same cell (meristemoid, initial) that gives rise to the guard cell initials, other subsidiary cells not arising from this meristemoid.

mesophanerophyte (Gr. mesos: in the middle; phaneros: visible, manifest; phyton: plant) n. A phanerophyte of size between 12 and 24 meters (37 and 73 feet).

mesophyll (Gr. mesos: in the middle; phyllon, leaf) n. The internal tissue of a leaf blade (lamina), consisting of parenchyma cells. There are two distinct forms. Palisade mesophyll lies just beneath the upper epidermis and consists of cells elongated at right angles to the leaf surface. They contain a large number of chloroplasts and their principal function is photosynthesis. Spongy mesophyll occupies most of the remainder of the lamina. It consists of spherical loosely arranged cells containing fewer chloroplasts than the palisade mesophyll. Between these cells are air spaces leading to the stomata. Of vegetation, characteristic of moist habitats and with soft, fairly large leaves predominating; a leaf whose area is within the approximate range between 20 and 180 square cm.

mesophyte (Gr. mesos: in the middle; phyton: plant) n. Any plant adapted to grow in soil that is well supplied with water and mineral salts. Such plants wilt easily when exposed to drought conditions as they are not adapted to conserve water. The majority of flowering plants are mesophytes. Cf. halophyte, hydrophyte, xerophyte.

mesophytic (Gr. mesos: in the middle; phyton: plant) adj. Adapted to a moderately humid habitat.

mesosperm (Gr. mesos: in the middle; sperma: seed) n. The middle layer of the coat of a seed. Cf. secundine.

mestome sheath The inner and endodermal layer of cells - the walls being thick and with suberized lamellae - of a two-layered bundle sheath surrounding a vascular bundle.

mesostylous (Gr. mesos: in the middle; stylos: column) adj. Having styles intermediate in length. Cf. macrostylous, microstylous.

mesotonic (Gr. mesos: in the middle; tonos: strength) adj. Of growth that neither intensified in the lower part (as in a basotonic plant) or the upper part (as in an acrotonic plant) of a plant, resulting in a columnar appearance of the plant.

mesotrophic adj. A term applied to clear water lakes and ponds with beds of submerged aquatic plants and medium levels of nutrients. These lakes are also of intermediate clarity, depth and temperature.

Mesozoic n. The middle of three eras that constitute the Phanerozoic period of time. The Mesozoic (literally 'middle life') was preceded by the Palaeozoic Era and followed by the Cenozoic Era. It began with the Triassic approximately 245 million years ago and ended around 65 million years at the start of the Tertiary. The Mesozoic comprises the Triassic, Jurassic, and Cretaceous Periods.

Messinian n. 1. The final age in the Miocene epoch, preceded by the Tortonian, followed by the Zanclian (Tabianian), and with its upper boundary dated at 5.2 million years ago. 2. The name of the corresponding European stage, which is roughly contemporaneous with the upper Mohnian and lower Delmontian (N. America), upper Tongaporutuan and lower Kapitean (New Zealand), and part of the Mitchellian (Australia). The neostratotype is found between Caltanisetta and Enna, Sicily. It is an important stage, marked by the presence of thick evaporite deposits in the Mediterranean. These may indicate that the Straits of Gibraltar were closed approximately 6.5 to 5.1 million years ago and that the Mediterranean was reduced to a series of evaporite basins.

metabolic adj. Of or pertaining to metamorphosis; pertaining to, or involving change. Of or pertianing to metabolism.

metabolism n. The sum of all physical and chemical processes by which living arganised substance is produced and maintained (anabolism) and also the transformation by which energy is made available for the uses of the organism (catabolism).

metabolite n. Any substance produced by metabolism or by a metabolic process.

metamorphosis n. A marked change in appearance, character, condition, or function. A change in the form and often habits of an animal during normal development after the embryonic stage. Metamorphosis includes, in insects, the transformation of a maggot into an adult fly and a caterpillar into a butterfly and, in amphibians, the changing of a tadpole into a frog.

metandry (Gr. meta: after; anęr, andros: male) n. Female flowers maturing before the male flowers, i.e. the male flowers maturing before the female flowers; protogyny.

metaphase n. The stage of cell division in which chromosomes are arranged in an equatorial plate or plane.

metaphyte (Gr. meta: after; phuton: plant) n. A multicellular plant.

metaxenia n. The influence of pollen on maternal tissues of the fruit. Cf. xenia.

metaxylem (Gr. meta: after; xylon: wood) n. The part of the primary xylem that develops in a plant after the stem or other part has finished elongating. The walls of the metaxylem are more extensively lignified than those of the protoxylem. Cf. protoxylem.

Metazoa (Gr. meta: after; zôon: any living being) n. In traditional classification systems, a subkingdom of animals whose bodies consist of many cells differentiated and coordinated to perform specialized functions. It excludes the single-celled protozoa and the Parazoa. In modern classifications, the protozoa are placed in the kingdom Protoctista and the animal kingdom is divided into the subkingdoms Parazoa and Eumetazoa.

metazoan (Gr. meta: after; zôon: any living being) n., adj. An animal of the subkingdom Metazoa, having a multicellular body and differentiated tissues and comprising all animals except protozoa and sponges. Of or relating to this subkingdom.

meteoric water Water precipitated from the atmosphere, as opposed to juvenile water.

methyl glucosinolates A class of aliphatic, straight chain glucosinolates. See also sinapine.

methylflavone n. A derivative of a chalcone.

metric trait A characteristic that shows continuous variation and may be determined by the interaction of polygenes and environments and in some cases by one of the monogenes when the environmental effect on the expression of the trait is large.

mevalonic acid A carboxylic acid precursor of sterols, terpenes and other isoprenoids.

micro- (Gr. mikros: small) prefix. Meaning small.

microclimate n. The atmospheric conditions affecting an individual or a small group of organisms, esp. when they differ from the climate of the rest of the community; the entire environment of an individual or small group of organisms.

microconidia See microconidium.

microconidium n. (pl. microconidia) Small spherical asexual spores produced from vegetative hyphae.

microenvironment n. The environment of a small area, such as that around a leaf or plant.

micro-evolution (Gr. mikros: small; L. evolutio: unfolding, unrolling) n. Evolution resulting from a succession of relatively small genetic variations that often cause the formation of new subspecies. Evolutionary change within species, which results from the differential survival of the constituent individuals in response to natural selection. The genetic variability on which selection operates arises from mutation and sexual reshuffling of gene combinations in each generation. Also microevolution.

microfossil n. A fossil generally less than 0.5 millimetre in size, such as a protozoan, bacterium, or pollen grain.

microgametophyte (Gr. mikros: small; gametęs: spouse; phyton: plant) n. A plant body or cell lineage, formed by vegetative growth of the microspore, that produces the male gametes of a heterosporous plant.

microhabitat n. A very small, specialized habitat, such as a clump of grass or a space between rocks.

micronema (Gr. mikros: small; nęma: thread) n. (pl. micronemata) Small, thin, sparsely branched rhizoids produced on stem between leaves. Cf. macronema.

micronemata See micronema.

micronemous (Gr. mikros: small; nęma: thread) adj. Having short filaments.

micronutrient A substance, such as a vitamin or mineral, that is essential in minute amounts for the proper growth and metabolism of a living organism.

microphanerophyte (Gr. mikros: small; phaneros: visible, manifest; phyton: plant) n. A phanerophyte of size between 3 and 12 meters (9 and 37 feet).

microphyll (Gr. mikros: small; phyllon: leaf) n. A type of foliage leaf in clubmosses and horsetails that has a single unbranched midrib. Such leaves are generally no more than a few millimetres long. Cf. megaphyll.

microphyllidious (Gr. mikros: small; phyllon: leaf) adj. Small, leaf-shaped.

microphylline adj. With minute leaflets or leafy scales.

microphyllous (Gr. mikros: small; phyllon: leaf) adj. Having small leaves, microphyllous branches produce smaller than normal leaves.

microphyte (Gr. mikros: small; phyton: plant) adj. A microscopic plant.

microphytic adj. See microphyte.

micropropagation n. The in vitro propagation of plants by cloning. Typically, this involves culturing excised meristematic tissue on a special medium that encourages axillary bud development. The new shoots are then separated and cultured, and the cycle is repeated until finally the shoots are transferred to a medium that promotes root development, to produce plantlets. Micropropagation is used in agriculture, horticulture, and forestry as special genotypes can be bred and maintained, the process is rapid, and plants can be kept disease-free. See also clone.

micropyle (Gr. mikros: small; pylę: door, way) n. A small opening in the integuments of a plant ovule through which the pollen tube passes prior to fertilization. It results from the incomplete covering of the nucellus by the integuments. It remains as an opening in the testa of most seeds through which water is absorbed, persisting as a pore in the seed coat.

microtubule n. A hollow cylindrical structure in the cytoplasm of most cells, involved in intracellular shape and transport.

microsporangia See microsporangium.

microsporangium (Gr. mikros: small; spora: seed; aggeion: vase, bowl, container) n. (pl. microsporangia) The smaller of the two kinds of sporangia produced in the sexual life cycle of a heterosporous plant.

microspore (Gr. mikros: small; spora: seed) n. The smaller of the two kinds of spores produced in the sexual life cycle of a heterosporous plant, giving rise to the male gametophyte. The smaller of the two kinds of spore produced by some ferns. Cf. megaspore.

microsporocyte n. A sporocyte giving rise by a meiotic division to (usually) four microspores.

microsporogenesis n. The sequence of meiotic divisions that produces microspores.

microsporophyll (Gr. mikros: small; sporos: seed; phyllon, leaf) n. A specialised leaf upon (or in the axil of) which one or more microsporangia are borne; a stamen.

microstomous adj. Having a small capsule mouth.

microstylous (Gr. mikros: small; stylos: column, pilar) adj. Having short styles. Cf. macrostylous, mesostylous.

micton n. A species of wide distribution, the result of hybridization of two or more species; all individuals are inter-fertile and have ancestral genotypes; apomixis is not present.

middle lamella The central layer of the wall between two adjacent cells, largely made up of pectinaceous substances.

midlobe n. The central lobe.

midnerve n. The central nerve.

midrib n. The central, and usually the most prominent, vein of a leaf or leaf-like organ; a mid-vein or single costa of a leaf or thallus.

midvein n. The principal vein in the blade of leaf, pinnule or segment.

mildew n. A growth of minute powdery or webby fungi, whitish or of different colors, found on various diseased or decaying substances.

miltanthaline n. A benzylisoquinoline alkaloid.

mimosiform (mimosa; L. forma: shape) adj. With round or conical flower heads having inconspicuous sepals and petals but conspicuous stamens, as found in the genus Mimosa. Syn. mimosoid.

mimosoid (mimosa; Gr. eidô: to look like) See mimosiform.

minerotropic adj. Said when the majority of the water comes from ground water sources.

minimum viable population A viable population is a population capable of maintaining itself, without significant manipulation. A minimum viable population is an estimate of the smallest viable population that will persist for a specified length of time (e.g. 500 years) and with a specified level of certainty (e.g. 95 %); the isolated population of least numbers which has a good chance of surviving despite the foreseeable effects of demographic, environmental, and genetic events and natural catastrophes.

Miocene (Gr. meioô: to reduce; kainos: new) n. Fourth of the five epochs of the Tertiary Period, extending from the end of the Oligocene, 23.3 million years ago, to the beginning of the Pliocene, 5.2 million years ago. Many mammals with a more modern appearance evolved during this epoch, including deer, pigs, and several elephant stocks. The Miocene comprises the Aquitanian, Burdigalian, Early and Late Langhian, Serravallian, Tortonian, and Messinian Ages.

miosis See meiosis.

mire n. Synonymous with any peat-accumulating wetland; area of swampy ground.

mischoblastiomorph n. A specialised thick-walled spore found in Rinodina.

Mississippian n. 1. The Early Carboniferous subperiod which is followed by the Pennsylvanian and comprises the Tournaisian, Visean, and Serpukhovian Epochs. It is dated at 362.5 to 322.8 million years ago. 2. The name of the corresponding N. American sub-system which comprises the Kinderhookian, Osagean, Meramecian, and Chesterian series. It is roughly contemporaneous with the Dinantian plus the Namurian A of western Europe.

Missourian n. A series in the Pennsylvanian of N. America, underlain by the Desmoinesian, overlain by the Virgilian, and roughly contemporaneous with the Krevyakinskian and lower Chamovnicheskian Stages of the Kasimovian Series.

mitochondria See mitochondrion.

mitochondrial See mitochondrion.

mitochondrion (Gr. mitos: thread; khondrion, diminutive of khondros grain) n. (pl. mitochondria) Any of various round or long cellular organelles of most eukaryotes that are found in varying numbers outside the nucleus, and that produce energy for the cell through cellular respiration; mitochondria are rich in fats, proteins, and enzymes and contain ATP, ATP and enzymes being involved in the cell's metabolic activities; each mitochondrion is bounded by a double membrane, the inner being folded inwards to form projections (cristae). (Syn. chondriosome)

mitogen n. An agent that induces mitosis.

mitogenic See mitogen.

mitosis (Gr. mitos: thread) n. Cell division in which the number of chromosomes in the daughter cells is the same as that of the parent cell. See also meiosis.

mitosporangia See mitosporangium

mitosporangium n. (pl. mitosporangia) A sporangium where spore formation occurs after mitosis.

mitosporic adj. Of spore formation after mitosis.

mitra n. The mitriform pileus of certain fungi; a galea

mitrate See mitriform.

mitriform (L. mitra: miter; froma: shape) adj. Shaped like a mitra; like the miter of a bishop, i.e. conic and undivided; e.g. Grimmia, Ptychomitrium. Also mitrate.

mixed bud A bud which produces both leaves and flowers.

mixed inflorescence An inflorescence with both racemose and cymose portions.

mixoploid adj., n. A chimera having different ploidy levels in the L1, L2, and L3 layers, as in 2-4-4, 4-4-2, and the like.

modioliform (L. modiolus; little cup, trough, axle; forma: shape) adj. Hollow, round and depressed, with a very narrow orifice; shaped like the hub of a wheel.

Mohnian n. A stage in the Upper Tertiary of the west coast of N. America, underlain by the Luisian, overlain by the Delmontian, and roughly contemporaneous with the upper Serravallian, Tortonian, and lower Messinian Stages.

molendinaceous (L. molindinum: [wind] mill) adj. With large, wing-like developments; in the form of a set of sails; with multiple projecting wings.

monad (Gr. monos: alone, single) n. A single individual that is free from other such individuals rather than being united into a group; a simple organism, e.g. one assumed as the first in the genealogy of living beings.

monadal adj. Of primitive type of morphological organisation in algae or unicellular flagellates.

monadelphous (Gr. monos: alone, single; adelphę: sister) adj. Of stamens united by the filaments into one bundle and forming a tube around the gynoecium; Of a plat or flower having the stamens so united..

monandrous (Gr. monos: alone, single; anęr, andros: male) adj. Of a flower with a single stamen; of a plnat with such flowers.

monanthous (Gr. monos: alone, single; anthos: flower) adj. One-flowered.

monaxial (Gr. monos: alone, single; axis: axle) adj. Uniaxial; having the flowers that grwo on the primary axis.

monecious See monoecious

Monera n. The former name for the kingdom containing all prokaryotic organisms. It includes all bacteria. It was one of the five kingdoms of life in the classification originally proposed by R. H. Whitaker (1959, 1969), comprising the prokaryotic Cyanophyta (blue-green algae) and Bacteria (Schizomycophyta). The bacteria were the first forms of life on Earth, dating from at least 3300 million years ago, while the first cyanophytes appeared about 2600 million years ago.

moniliform (L. monile: necklace; forma: shape) adj. Constricted laterally and appearing bead-like; contracted at short regular intervals like a string of beads, giving a beaded necklace-like appearance; terete with regular bulges.

monimioid adj. Said of a leaf tooth in which the secondary or tertiary vein ends in an opaque persistent glandular cap, not associated with lateral veins.

monistichous adj. Arranged in a single vertical row along the stem (orthostichy); one-ranked. Also monostichous.

mono- (Gr. monos: alone, single) prefix. Meaning one, alone, single.

monocarp (Gr. mono: alone, single; karpos: fruit) n. A plant that dies after having once borne fruit.

monocarpellary (Gr. mono: alone, single; karpos: fruit) adj. Consisting of a single carpel.

monocarpic (Gr. mono: alone, single; karpos: fruit) adj. Flowering and fruiting only once during its life span.

monocarpous (Gr. mono: alone, single; karpos: fruit) adj. With one carpel, i.e. having a gynoecium which forms only a single ovary. Bearing fruit only once during its life span, i.e. monocarpic.

monochasia See monochasium.

monochasial adj. With the form of a monochasium.

monochasium (Gr. monos: alone, single; kazo: separate) n. (pl. monochasia) A cymose inflorescence with the branches arising singly, i.e. with only a single main axisi; a cyme having a single flower on each axis. Cf. dichasium.

monochlamydeous (Gr. monos: alone, single; khlamis: cloak, mantle) adj. Of a flower, having only one whorl of perianth parts. Syn. haplochlamydeous.

monochromatic (Gr. monos: alone, single; khrôma: color) adj. Of a single color

monoclinous (Gr. monos: single, alone; klinę: bed) adj. Having both stamens and pistils in the same flower; perfect.

monocolpate adj. Refers to pollen grains with a single furrow.

monocot n. See monocotyledon.

monocotyledon (Gr. monos: alone, single; kotylędon: cavity, hollow) n. A plant of the class Liliidae of the Magnoliopsida that has one seed leaf (cotyledon) in its seeds. Monocotyledonous plants typically have strap-like parallel-veined leaves, and floral parts arranged in multiples of three or six. Examples are cereals, fodder grasses, lilies and orchids. Cf. dicotyledon. Also monocot.

Monocotyledonae (Gr. monos: alone, single; kotylędon: cavity, hollow) n. One of the two classes of flowering plants (see Anthophyta), distinguished by having one seed leaf (cotyledon) within the seed. The monocotyledons generally have parallel leaf veins, scattered vascular bundles within the stems, and flower parts in threes or multiples of three. Monocotyledon species include some crop plants (e.g. cereals, onions, fodder grasses), ornamentals (e.g. tulips, orchids, lilies), and a very limited number of trees (e.g. the palms). Cf. Dicotyledonae.

monocotyledonous (Gr. monos: alone, single; kotylędon: cavity, hollow) adj. With a single cotyledon.

monocyclic (Gr. monos: alone, single; kyklos: circle) adj. With a single whorl.

monodynamous adj. With one stamen distinctly larger than the others.

monoecious (Gr. monos: single; oikos: house) adj. Describing plant species that have separate male and female flowers on the same plant; examples of monoecious plants are maize and birch; in bryophytes: with antheridia and archegonia on the same plant. Cf. dioecious. Syn. monecious, monoicous.

monoecy (Gr. monos: single; oikos: house) n. The fact of being monoecious.

monoembryonic adj. Refers to seeds or ovules with a single germ cell or embryo; e.g. the mango.

monogeneric adj. Refers to a family or taxon of higher rank made up of a single genus.

monogenesis n. Origin of diverse individuals or kinds by descent from a single ancestral individual or kind. The production of similar organisms in successive generations.

monogenetic adj. Relating to or involving monogenesis. Having a single host through the course of the life cycle. Of a a family with a single genus.

monogynoecial (Gr. monos: alone, single; gynę: female; oikos: house) adj. Of a fruit developing form a single pistil.

monogynous (Gr. monos: alone, single; gynę: female) adj. With one carpel; having only one pistil.

monohybrid adj., n. Heterozygous with respect to one gene.

monoicous See monoecious.

monolete adj. Describing spores having a single laesura, i.e. a single, unbranched, linear scar one the surface that marks the point of attachment in the tetrad; e.g. the spores of Funaria hygrometrica and Bryum caespiticium, of Dryopteris. See spore. Cf. trilete.

monolocular (Gr. monos: alone, single; L. loculus: little box) adj. With a single cell or chamber; unilocular.

monomerous (Gr. monos: alone, single; meros: part) adj. With a single member, as in a floral whorl with only one part

monomial adj., n. (Of) a taxonomic name consisting of a single word, such as genus, e.g. Iris, or family, e.g. Iridaceae.

monomorphic (Gr. monos: alone; morphę: shape) adj. Having one shape; with a single form; all alike in appearance.

monopetalous (Gr. monos: alone; petalon: leaf) adj. Having a corolla fused into one piece, or the petals fused into a tube. Syn. gamopetalous.

monophyletic (Gr. monos: alone; phylę: tribe) adj. If the members of a given taxon are descended from a common ancestor they are said to be 'monophyletic', e.g. the families within a class would be monophyletic if they were all descended from the same family or lower taxonomic unit. Under the strictest definition they would all have to be descended from a single species. A monophyletic group is called a clade. Cf. polyphyletic.

monophyletic group See monophyly.

monophyllous (Gr. monos: alone, single; phyllon: leaf) adj. Of a single leaf; with simple leaves; said of plants that have simple leaves though their relatives have compound leaves. Consisting of a single lobe, often undulate or folded.

monophyly n. Term applied to a group of organisms that include an ancestor and all of its descendants; cf paraphyly, paraphyletic groups, polyphyly, polyphyletic groups.

monoploid adj., n. Having a single set of chromosomes; haploid. A monoploid cell or organism.

monopodia See monopodium.

monopodial (Gr. monos: alone, single; pous, podos: foot) adj. Of growth, with a persistent terminal growing point producing many lateral organs successively; a type of branching in which lateral branches arise from a definite main, central stem; with a single axis, an extension growth from the apex; of a stem, growing in the above manner. Cf. sympodial.

monopodium (Gr. monos: alone, single; pous, podos: foot) n. (pl. monopodia) The main axis of a stem or rhizome that maintains a single direction of growth, form the tip, and gives off lateral branches or stems in acropetal succession; the primary axis of growth in such plants as pine trees. Cf. sympodium.

monopterous (Gr. monos: alone, single; pteron: wing) adj. With a single wing.

monosaccate adj. Of a pollen grain with one saccus or buoyant bladder.

monosepalous (Gr. monos: alone, single; skepas: covering, shelter; [pe]talon: leaf) adj. See gamosepalous.

monosome n. A Diploid organism that lacks one chromosome of its proper complement; `monosome' refers to a single chromosome, `disome', to two chromosomes of a kind, and `trisome' to three chromosomes of a kind.

monosomic adj. See monosome.

monospecific adj. Refers to a genus which has a single species.

monospermous (Gr. monos: alone, single; sperma: seed) adj. One-seeded; producing a single seed.

monostelic adj. Having one stele; cf. polystelic.

monostichous (Gr. monos: alone, single; stikhos: line, row) adj. With flowers arranged in a single spike, i.e. in a single vertical rank, layer or row. Also monistichous.

monostromatic adj. Of one cell layer in thickness; e.g. most bryophyte leaf blades and certain thalli or thallus wings.

monostylous (Gr. monos: alone, single; stylos: column, pilar) adj. With a single style.

monosymmetric adj. Said of a flower with a single plane of symmetry. Also monosymmetrical.

monosymmetrical (Gr. monos: alone, single; symmetria: right proportion, symmetry) adj. Bilaterally symmetrical; zygomorphic. Also monosymmetric.

monotelic adj. Said of inflorescences, same as determinate.

monoterpene See monoterpenes.

monoterpenes n. pl. A terpene with two isoprene units. See terpenes.

monoterpenoid n. Occurs in essential oils and is made up of one or two isoprene rings or an open chain of isoprene units; colorless, water-insoluble, volatile, with fragrant odour.

monotrichous (Gr. monos: alone, single; thrix, trikhos: hair, bristle) adj. With a single bristle

monotype (Gr. monos: alone, single; typos: mark, image) n. The sole member of its group, such as a single species that constitutes a genus.

monotypic (Gr. monos: alone, single; typos: mark, image) adj. In classification, a taxon with only a single representative, as a genus with a single species or a family with a single genus, etc.; thus a phylum may have only a single class or order and might be represented by a single genus and species. Cf. polytypic.

montane (L. montanus: of mountain) adj. Of a plant growing in the mountains, the cool moist upland regions below timber line.

moor n. A broad area of open land, often high but poorly drained, with patches of heath and peat bogs. A boggy area, especially one that is peaty and dominated by grasses and sedges.

morphine n. An alkaloid present in opium (see opiate). It is an analgesic and narcotic, used medically for the relief of severe pain.

morphocline n. A sequence of character states, each of which is logically derivable from its neighbor in the sequence; a graded series of character states of a homologous character.

morphodeme n. A group of individuals in a taxon that is morphologically differentiated from the rest of the taxon by a characteristic of undetermined or no taxonomic significance.

morphologic adj. See morphology. Also morphological.

morphological adj. See morphology. Also morphologic.

morphologically adv. See morphological.

morphology (Gr. morphę: shape, form; logos: word, reason) n. A branch of biology that deals with the form and structure of animals and plants, a study of the forms, relationships, metamorphoses, and phylogenetic development of organs apart from their functions. The study of shape and form in organisms.

morphometrics n. Method to define and describe morphological characters and character states based on quantifiable measurements; morphometrics can also help define form taxa by evaluating ranges of variation within and between groups.

Morrowan n. A series in the Pennsylvanian of N. America, underlain by the Chesterian (Mississippian), overlain by the Atokan, and roughly contemporaneous with the Bashkirian Series.

mosaic n. A viral disease of plants, resulting in light and dark areas in the leaves, which often become shriveled and dwarfed. Also mosaic disease.

mosaic disease See mosaic.

moschate adj. With a musky scent.

moss n. A cryptogamous plant of a cellular structure, with distinct stem and simple leaves. The fruit is a small capsule usually opening by an apical lid, and so discharging the spores. There are many species, collectively termed Musci, growing on the earth, on rocks, and trunks of trees, etc., and a few in running water. The term moss is also popularly applied to many other small cryptogamic plants, particularly lichens, species of which are called tree moss, rock moss, coral moss, etc. Fir moss and club moss are of the genus Lycopodium.

mother cell A cell that divides to produce two or more daughter cells.

mother-cell See mother cell

motile (L. motus: motion) adj. Actively moving; self-propelled; capable of movement.

mottled adj. With variegated coloring. A surface having colored spots or blotches.

mucilage (L. mucilago: mucus) n. A gumlike, gelatinous, viscous, slimy substance frequently present in the cell walls of aquatic plants (as seaweeds), in the seed coats of certain other species (as legumes), and exuded by certain plants or plant organs. Mucilages are hard when dry and slimy when wet. Like gums they probably have a general protective function or serve to anchor the plant. Mucilage contains protein and polysaccharides and is similar to plant gums.

mucilaginous (L. mucilago: mucus) adj. Having mucilage; and moist.

Mucor (L. mucor: mould) n. A genus of mould fungi commonly seen on dead and decaying organic matter. They can be pathogenic in man.

mucosa n. A membrane lining all body passages that communicate with the air, such as the respiratory and alimentary tracts, and having cells and associated glands that secrete mucus. Also called mucous membrane.

mucous adj. Of, pertaining to, or resembling, mucus; slimy, ropy, or stringy, and lubricous; as, a mucous substance. Secreting a slimy or mucigenous substance, as the mucous membrane.

mucous membrane See mucosa.

mucro (L. mucro, mucronis: sharp point) n. (pl. mucrones) A stiff or sharp point abruptly terminating an organ; usually at the tip of a leaf; a small awn. Cf. apiculus.

mucronate (L. mucronatus: ending, tapered in a point) adj. Said of a leaf or other organ ending suddenly with a stiff spine as a continuation of the midrib; tipped with a mucro. Syn. mucronated.

mucronated See mucronate.

mucrones See mucro.

mucronulate (diminutive of L. mucronatus: ending, tapered in a point) adj. Diminutive of mucronate; tipped with a very small mucro.

multi- (L. multus: many) prefix. Meaning many.

multicellular adj. Consisting of, or having, many cells or more than one cell.

multiciliate (L. multus: many; cilium: eyelid, eyelash, eyebrow) adj. With many cilia.

multicipital (L. multus: many: caput, capitis: head) adj. Many-headed, as the crown of a root divided into a number of caudices; having many heads or many stems from one crown or root.

multicostate (L. multus: many; costa: rib, side) adj. With many ribs.

multifid (L. multus, much, many; findere, to cleave) adj. Cleft into many narrow segments or lobes; divided into many parts. Syn. multipartite.

multiflorous (L. multus: many; flos, floris: flower) adj. Bearing many flowers. Also multiflorus.

multiflorus See multiflorous.

multifoliate (L. multus: many; folia: leaf) adj. Bearings many leaves or leaflets.

multilacunar adj. Said of nodal anatomy in angiosperms, where more than three (e.g. 5, 7) leaf gaps are left in the central vascular cylinder when corresponding numbers of leaf traces depart.

multiline varieties Two or more isogenic lines of normally self-fertilizing plants that are similar in most characteristics but differ in a limited number of describable physiological, morphological, or other essential or distinctive characteristics; derived by growing the component lines separately and compositing the lines to constitute the breeder class of seed. Examples: `Multiline E-69' oat, `Miramar-63' wheat.

multiparous (L. multus: many; parere: to produce) adj. Producing many, or more than one, at a birth. A cyme with many lateral axes.

multipartite (L. multus: many; pars, partis: part) adj. See multifid.

multiperennial (L. multus: many; lasting the whole year) adj. Monocarpic but living several to many years before flowering, as in Agave. See pliestesial.

multiple fruit A fruit formed from several separate flowers crowded on a single axis, as a mulberry or pineapple.

multiplicate (L. multus: many; plicatus: folded) adj. Repeatedly folded.

multiplicative adj. Said of integuments (i.e. tegmen, testa) in seeds, where cell division and hence increase in thickness occur after fertilisation.

multiradiate (L. multus: many; radiatus: with rays, beams) adj. With many rays.

multiseptate (L. multus: many; septum: fence, partition) adj. With many septae or partitions.

multivalent See univalent.

muricate (L. muricatus: filled with sharp points) adj. Having a rough surface texture owing to small, sharp projections; covered with short, hard tubercles.

murication (L. muricatus: filled with sharp points) n. A small, sharp projection or point

muriculate (diminutive of L. muricatus: filled with sharp points) adj. Rough with minute, short, hard points; very finely muricate.

muriform (L. murus: wall; forma: shape) adj. Resembling courses of bricks or stones in squareness and regular arrangement, as a muriform variety of cellular tissue; divided into many chambers.

muscariform (L. muscarium: horse tail; forma: shape) adj. Brush-shaped; penicillatate.

muscicolous adj. Growing on mosses.

muskeg n. In the northern United States and Canada: a swamp or bog in an undrained or poorly drained area of alluvium or glacial till, or, more especially, in a rocky basin filled with water-saturated muck, decayed vegetal matter, and sphagnum moss incapable of sustaining much weight. The surface is commonly hummocky. In Alaska: more widely applied to any mossy and swampy ground regardless of topographic environment.

mutagen n. An agent, such as a chemical, ultraviolet light, or a radioactive element, that can induce or increase the frequency of mutation in an organism.

mutagenic adj. See mutagen.

mutant (L. mutatus: changed, moved) adj., n. Resulting from or undergoing mutation: a mutant strain of bacteria. An individual, organism, or new genetic character arising or resulting from mutation.

mutation n. A sudden variation that is inherited; the term is used loosely to include `point mutations' of a single gene and chromosomal changes. Any error in the duplication (copy) of the genetic material of a cell or an organism, which is transmitted to part of its descent. While most mutations are neutral, i.e. don't have any significant effect on individuals (phenotypes), some modify significantly their reproductive success. These are retained or eliminated by natural selection.

muticous (L. muticus: mutilated, curtailed) adj. Blunt, without a point, awn or spine.

mutualism (L. mutuus: reciprocal, mutual) n. An interaction between two species in which both species benefit. (The term symbiosis is often used synonymously with mutualism.) A well-known example of mutualism is the association between termites and the specialized protozoans that inhabit their guts. The protozoans, unlike the termites, are able to digest the cellulose of the wood that the termites eat and release sugars that the termites absorb. The termites benefit by being able to use wood as a foodstuff, while the protozoans are supplied with food and a suitable environment. See also mycorrhiza.

mycelia See mycelium.

mycelial adj. See mycelium.

mycelium (Gr. mykęs: fungus) n. (plural mycelia) A network of hyphae that forms the body of a fungus. It consists of feeding hyphae together with reproductive hyphae, which produce sporangia and gametangia. The hyphae are thread-like structures, consisting of a hyphal wall containing membrane-bound cytoplasm. They may be divided by cross-walls into discrete sections, depending on the type of fungus.

mycobiont n. The fungal component of a lichen.

myco-heterotroph n. The parasitic plant partner in a myco-heterotrophy relationship. Myco-heterotrophy is considered a kind of cheating relationship and myco-heterotrophs are sometimes informally referred to as 'mycorrhizal cheaters'.

myco-heterotrophy n. A symbiotic relationship between certain kinds of plants and fungi, in which the plant gets all or part of its food from parasitism upon fungi rather than from photosynthesis.

mycologic adj. Of or relating to mycology, or the fungi. Also mycological.

mycological adj. See mycologic.

mycologically adv. See mycological.

mycologist n. See mycology.

mycology (Gr. mykęs: fungus; logos: word) n. The branch of botany that deals with mushrooms and fungi. The mushrooms and fungi native to a region. The composition or characteristics of a particular mushroom or fungus: the mycology of rusts and mildews.

mycophagy n. The use of fungi as food.

mycoplasma n. A genus of bacteria which lack a cell wall.

mycoplasmic adj. See mycoplasma.

mycorhizae A plural of mycorrhiza.

mycorhizal See mycorrhizal.

mycorrhiza (Gr. mykęs: fungus; riza: root) n. (pl. mycorrhizae, mycorrhizas) An association between a fungus and the roots of a higher plant that is beneficial to both participants. In some mycorrhizas the fungus forms a sheath around the root, with its hyphae penetrating between the root cells; in others the fungus lives between and within the root cells. The plant benefits by more efficient uptake of nutrients, and the fungus obtains carbohydrates and other nutrients from the plant. Certain mycorrhizal associations between grasses and basidiomycete fungi can produce fairy rings of toadstools on the soil surface. Also mycorhiza.

mycorrhizae See mycorrhiza

mycorrhizal adj. See mycorrhiza. Also mycorhizal.

mycotrophe n. See mycotrophic.

mycotrophic (Gr. mykęs: fungus; trophę: food) adj. Modified by a mycorrhizal relationship. Some flowering plants do not have photosynthetic chlorophyll-bearing (green) leaves and are completely parasitic on the stems and roots of other plants. In order to grow and reproduce, they must absorb their vital carbohydrates (sugars) and amino acids from the host plant. Some of these root and stem parasites include the most bizarre plants on earth. Since they are nonphotosynthetic, they are also called heterotrophic like most animals and humans. Some heterotrophic plants look more like pale, fleshy fungi than flowering plants. They live in the deep humus of shady forests and include some very strange and colorful species. These fungus flowers are referred to as mycotrophic (fungus-nutrition) because their carbohydrates and amino acids come from mycorrhizal soil fungi which are in turn attached to the roots of nearby forest trees. Like true parasitic flowering plants, mycotrophic wildflowers must absorb their energy-rich molecules from other host plants, but unlike the direct root and stem parasites, their carbohydrates and amino acids are derived from nearby root systems via a conduit of filamentous soil fungi. Using labeled sugars containing radioactive carbon 14, scientists have shown that carbohydrates synthesized by nearby trees pass into the mycorrhizal soil fungi and eventually into the mycotrophic fungus flowers.

myochrous (Gr. mys, myos: mouse; khrôma: color) adj. Mouse-colored.

myricetin n. A common flavonol.

myristic acid A saturated 14-carbon fatty acid, CH3 (CH2)12 COOH, occurring in many fats.

myrmecochores (Gr. myrmęx, myrmękos: ant; khôreô: to move) adj. Dispersed by ants. Also myrmecochorous. See myrmecochory.

myrmecochorous adj. See myrmecochores.

myrmecochory (Gr. myrmęx, myrmękos: ant; khôreô: to move) n. The collection and dispersal of plant seeds by ants. A variety of plant species possess hard seeds that are inedible to ants but are nevertheless gathered by them and taken to the ants' nest. The ants perform this service because the seeds are equipped with special food bodies (elaiosomes). These are variously shaped appendages derived from ovarian tissue and containing proteins, lipids, and carbohydrates. In the nest the ants detach the elaiosomes and feed them to their larvae, discarding the seeds either within or near the nest. The ant benefits by receiving food, while the seed dispersal may benefit the plant in several ways: for example, protection of the seeds inside the ants' nest; reduction of competition from its own seedlings; or removal of the seeds to a suitable germination site.

myrmecophile (Gr. myrmęx, myrmękos: ant; philos: friend) adj. An organism, such as a beetle, a plnat, that habitually shares the nest of an ant colony. Also myrmecophilous.

myrmecophilous See myrmecophile.

myrmecophily n. See myrmecophile.

myrmecophyte A plant that lives in association with a colony of ants and possesses specialized organs in which the ants live. For example, Myrmecodia, an epiphytic plant from Malaysia, develops root tubers containing a network of cavities inhabited by ants.

myrosinase n. The enzyme that breaks down glucosinolates, yielding distinctive isothiocyanates.