tachytelic (Gr. takhys: fast; telikos: tending to a definite end) adj. Of or pertaining to evolution at a rate faster than the standard for a given group of plants or animals. Cf. bradytelic, horotelic.

tachytely n. See tachytelic

tadpole n. The limbless aquatic larva of a frog or toad, having gills and a long flat tail. As the tadpole approaches the adult stage, legs and lungs develop, and the tail gradually disappears. Also called polliwog.

taenia (Gr. tainia: bandage) n. Formation of ribbon-like structure with little or no differentiation between the leaf blade and stem.

taeninate (Gr. tainia: bandage) adj. Tapeworm-shaped; long and irregularly contracted.

tailed adj. With a tail-like appendage or appendages.

tannic acid See tannin

tannin n. One of a group of complex organic chemicals, phenol derivatives, glucosides, commonly found in leaves, unripe fruits, galls of many plants and the bark of trees. Their function is uncertain, possibly giving protection or concerned with pigment formation, though the unpleasant taste may discourage grazing animals. Some tannins have commercial uses, notably as mordants for many dyes, in the production of leather (tanning) and ink. Syn. tannic acid.

tapeta See tapetum.

tapetum n. (pl. tapeta) A nutritive layer of cells in the sporangium of ferns and anthers of flowering plants that surrounds developing spore cells.

taphrophilous adj. Thriving in ditches.

tap-root See taproot.

tapeworm n. Any of various ribbonlike, often very long flatworms of the class Cestoda, that lack an alimentary canal and are parasitic in the intestines of vertebrates, including humans.

taproot n. The main root of a plant, having a single, dominant axis, from which smaller root branches arise; a root system with a main root axis and smaller branches, as in most dicots. Cf. fibrous roots.

tap-rooted See taproot.

taprooted See taproot.

tartareous adj. Having a thick, rough, crumbling surface.

Tartarian See Changxingian

tassel n. Tassel-like flower-head of some plants, especially the staminate inflorescence in corn (Zea).

Tatarian See Changxingian

tautonym n. A taxonomic designation, such as Gorilla gorilla, in which the genus and species names are the same, commonly used in zoology but no longer in botany. An illegitimate binomial in which the genus and species are the same word, such as Amoracia armoracia, later changed to Armoracia rusticana.

tawny adj. Tan in color.

taxa See taxon.

taxic adj. Related to a taxon.

taxic homology Correspondence in structure between sister groups; for example fronds of ferns and leaves of dicots are taxic homologies, i.e. they are derived structures from the same primitive structure of the common ancestor of these two groups.

taxis n. A non-directional response of a plant to a stimulus, e.g. the response of the leaves or leaflets of Mimosa pudica to touch.

taxon (Gr. taxis: arrangement) n. (pl. taxa) A taxonomic category or unit, at any level, in a system for classifying plants or animals, as a species or genus.

taxonomic (Gr. taxis: arrangement; nomos: custom, law) adj. Related to taxonomy.

taxonomic synonym Any one of two or more different names based on different plant specimens which were later judged to belong to the same taxon.

taxonomically adv. See taxonomic.

taxonomist (Gr. taxis: arrangement; nomos: custom, law) n. A specialist in the naming and classification of organisms.

taxonomy (Gr. taxis: arrangement; nomos: custom, law) n. A science that includes identification, nomenclature, and classification of objects, and is usually restricted to objects of biological origin; orderly classification of plants according to their presumed natural relationships forming a basic biological discipline involving during its Linnean period the firm establishment of binomial nomenclature and acceptance of the static concept of fixity of the species, during its Darwinion period the dynamic concept of speciation by natural selection, and during its modern Mendelian epoch an expansion to include study of the mechanisms underlying speciation and related processes.

tectum (L. tectum: roof, shelter) n. The outermost layer of a pollen grain.

tegmen n. That part of the seed coat that develops from the inner integument.

tegule (L. tegula: tile) n. One of the bracts of the involucre in the Compositae (Asteraceae).

teleomorph n. The perfect (sexual) form of an anamorph; morphological structure of the sexual cycle.

teleutospore See teliospore.

teliospore n. A thick-walled, usually blackish resting spore of some rusts and smuts, from which the basidium arises. Also called teleutospore.

telmatophilous adj. Dwelling in wet meadows or marshes.

telophase n. The last stage in cell division before the nucleus returns to a resting condition.

temperate (L. temperatus: well controlled, moderate) adj. Distributed in those regions of the earth lying tween the tropic of Cancer and the Arctic Circle or between the tropic of Capricorn and the Antarctic Circle.

tendril n. A slender twining or clasping process, modified stem, leaf, leaflet, part of a leaf, stipule, by which some plants climb, or supports itself, by attaching its tendrils to some other body.

tendrillar adj. See tendril.

tendrilly adj. See tendril.

tendrilous adj. See tendril.

tendril-pinnate adj. Pinnately compound, but ending in a tendril, as in the sweet pea.

teniola n. (pl. teniolae) The intramarginal row (border) of differentiated cells in a leaf; generally more than one cell thick in the blade, always so in the base; e.g. Calymperes.

teniolae See teniola.

tension wood A kind of reaction wood containing gelatinous fibres with little or no lignification that are produced on the adaxial side of the branch-stem junction.

tentacle n. A sensitive filament, as the glandular hairs of Drosera.

tentacular adj. Bearing tentacles.

tenuinucellate adj. Said of an ovule in which no cell layers separate the megasporocyte or embryo sac from the epidermis.

tenuous (L. tenuis: thin, fine, slender) adj. Slender or thin

tepal n. A division of the perianth, a sepal or a petal, of a flower in which the calyx and corolla are almost identical in appearances and not readily differentiated; tepal are common in many groups of monocots, as in tulips and lilies. In Orchidaceae, this term refers to any sepal or petal, except the labellum.

tepui n. The Tepuis are table-like mountains (mesas) found only in the Guiana highlands. These geological formations tend to be found as isolated entities rather than in mountain range fashion, which makes them the host of a unique array of endemic plant and animal species. Some of the most outstanding tepuis are Autana, Pico da Neblina (the highest one, on the Venezuela- Brazil border), Auyantepui and Monte Roraima. They are typically composed of Precambrian sandstone rocks, very hard to climb, which rise abruptly from the jungle, giving rise to spectacular natural scenery. Auyantepui in particular is the source of Angel Falls, the world's tallest waterfall.

teratologic adj. See teratology.

teratological adj. See teratology.

teratology n. The biological study of birth defects; the branch of medical science concerned with the development of physical abnormalities during he fetal or early embryonic stage. The branch of biology that is concerned with the structure, development, etc., of monsters. A collection of tales about mythical or fantastic creatures, monsters, etc.

terete (L. teres, teretis: round, smooth) adj. Slender and smooth, with a circular transverse section; cylindrical or sligntly tapering.

tergeminate adj. Thrice divided into equal pairs; paired leaflets temately compound.

terminal (L. ter: three times; geminatus: doubled) adj. At the apex or distal end.

ternary (L. terni: by three, three each) adj. Consisting of threes or involving three, triple.

ternate (L. terni: by three, three each) adj. Growing in groups of threes, as some leaves; of a single leaf, having the leaflets arranged in groups of three.

ternately adv. See ternate.

terpene See terpenes.

terpenes n. Naturally occurring hydrocarbons found in the essential oils. Typically they are volatile compounds with pleasant odours and are used in flavouring foods and in perfumes. Terpenes are produced by many plants, particularly conifers. They are major components of resin, and of turpentine produced from resin. The name terpene comes from turpentine. Terpenes are derived from isoprene C5H8 units and have the basic formula of multiples of it, i.e., (C5H8)n. This is called the isoprene rule. The isoprene units can be arranged in a linear way or forming rings. One can consider isoprene as one of nature's preferred building blocks. Terpenes can be classified according to the number of isoprene units that they contain: . Monoterpenes, C10H16, 2 isoprene units . Sesquiterpenes, C15H24, 3 isoprene units . Diterpenes, C20H32, 4 isoprene units . Triterpenes, C30H48, 6 isoprene units . Tetraterpenes, C40H60, 8 isoprene units . Polyterpenes with a large number of isoprene units The important plant photosynthetic pigment carotene is a tetraterpene. Rubber is essentially a polyterpene If terpenes are further modified, for instance by adding hydroxyl groups or moving or removing a methyl group, the resulting compounds are called terpenoids. (Some authors also call these compounds terpenes.)

terpenoid adj., n. Pertaining to terpenes. Terpene.

terrestrial (L. terrestris: relative to earth) adj. Growing on ground; not aquatic.

terricolous adj. Growing on soil (terrestrial).

Tertiary (L. tertius: third) n. First sub-era of the Cenozoic era, which began about 65 million years ago and lasted until 1.64 million year ago. The Tertiary followed the Mesozoic and comprises five epochs: the Palaeocene, Eocene, Oligocene, Miocene, and Pliocene.

tesselate (L. tessalla: tile) adj. With a checkered pattern. Also tessellated.

tessellated See tesselate.

test See testa.

testa (L. testa: shell, brick, tile) n. (pl. testae) The lignified or fibrous protective covering of a seed that develops from the integuments of the ovule after fertilization. See also hilum; micropyle. Also test.

testaceous (L. testaceus: brick-colored) adj. Of a brick-red, brownish-red, or brownish-yellow color.

testae See testa.

testicular See testiculate.

testiculate (L. testiculus: testicle, testis) adj. In the form of two oblong bodies; shaped like a testis; having tuber shaped like testes, as certain orchids. Also testicular.

tetra- (Gr. tetras: four; L. tetras, tetradis: four) prefix. Meaning four.

tetracytic adj. Said of stomata, surrounded by four subsidiary cells, two or which are parallel to and two at right angles to the long axis of the guard cells.

tetrad (Gr. tetradion: union of four) n. A group of four; a group of four haploid cells formed at the end of the second division of meiosis; four pollen grains remaining fused together at maturity, e.g. in Ericaceae, Epacridaceae.

tetradinous (Gr. tetradion: union of four) adj. Occurring in tetrads.

tetradymous (Gr. tetradymos: quadruple) adj. With four cells

tetradynamous (Gr. tetras: four; dynamis: power) adj. Of an androecium, consisting of four stamens of the same length and two of a different length, as in most members of the Cruciferae (Brassicaceae).

tetragonal (Gr. tetragniaios: square, quadangular) adj. Four-angled.

tetrahedral (Gr. tetraedron: tetraedron) adj. Four-sided, each side triangular

tetramerous (Gr. tetras: four; meros: part) adj. With parts arranged in sets or multiples of four. Of a flower having four segments in each perianth whorl, and usually in each whorl of stamens also.

tetrandrous (Gr. tetras: four; anr, andros: male) adj. With four stamens.

tetrangular (L. tetras: four; angulus: angle) adj. With four angles.

tetrapetalous (Gr. tetras: four; petalon: leaf) adj. With four petals.

tetraploid (Gr. tetras: four; eid: to look like) adj, n. Describing a nucleus, cell, or organism that has four times (4n) the haploid number (n) of chromosomes. Cf. polyploid, diploid, haploid.

tetrapterous (L. tetras: four; pteron: wing) adj. With four wings or wing-like appendages.

tetrasepalous (L. tetras: four; skepas: covering, shelter; [pe]talon: leaf adj. With four sepals.

tetrasomic adj., Of an organism whose cells contain four chromosomes of one type; the rest of the chromosome complement is diploid (chromosome formula: 2n + 2). Cf. trisomic.

tetrasporangia See tetrasporangium.

tetrasporangium (L. tetras: four; spora: seed; aggeion: vase, bowl, container) n. (pl. tetrasporangia) A sporangium containing four asexual spores. A unicellular sporangium found in certain red algae in which four tetraspores are produced from meiosis.

tetrasporangiate adj. With a tetrasporangium.

tetraspore (L. tetras: four; spora: seed) n. One of the four spores produced within a tetrasporangium.

tetrasporic adj. See tetraspore.

tetrasporous adj. See tetraspore.

tetrastachyous (L. tetras: four; stakhys, stakhyos: ear of wheat) adj. With four spikes.

tetrastichous (L. tetras: four; stikhos: line, row) adj. Arranged in four vertical ranks or rows on an axis; having four such rows of flowers, as a spike.

tetraterpene See tetraterpenes.

tetraterpenes n. pl. A terpene with 8 isoprene units. See terpenes.

thalami See thalamus.

thalamic adj. See thalamus.

thalamically adv. See thalamus.

thalamous See thalamus.

thalamus (Gr. thalamos: room) n. (pl. thalami) A receptacle or torus; thallus. See thallus, receptacle.

thalli See thallus.

thalloid (Gr. thallos: young shoot; eid: to look like) adj., n. Of or resembling a thallus. Plants which have no roots, stems, or leaves such as liverworts and hornworts are called thalloid.

Thallophyta (Gr. thallos: young shoot; phyton, a plant) n. A primary division of plants including all forms consisting of one cell and cell aggregates not clearly differentiated into root, stem, and leaf, including bacteria, algae, fungi, and lichens.

thallophyte (Gr. thallos: young shoot; phyton, a plant) n. Any plant of the phylum (division) Thallophyta, in which the plant body of the larger species is typically a thallus.

thallophytic adj. See thallophyte.

thallose adj. Of or pertaining to a thallus.

thallus (Gr. thallos, a young shoot) n. (pl. thalli, thalluses) A plant body that is characteristic of thallophytes, lacks differentiation into distinct members (as stem, leaves, and roots), and does not grow from an apical point e.g. multicellular algae, some bryophytes (particularly the gametophytes of many liverworts), and Lemnaceae. In cryptogams, a cellular expansion taking the place of stem and foliage and forming the main body fungi and lichens.

thalluses See thallus.

theca (Gr. thk: box, case) n (pl. thecae) A part of a plant serving as a receptacle. A pollen sac or cell of the anther. The spore-bearing portion of a moss capsule. The spore case of a fungus (sporangium).

thecae See theca.

thecate (Gr. thk: box, case) adj. Having or being contained in a theca.

thecia See thecium.

thecial adj. See thecium.

thecium (Gr. thk: case, box) n. (pl. thecia) Hymenium.

thelephoroid (Gr. thl: nipple; phora: carrying; eid: to look like) See thelephorous.

thelephorous (Gr. thl: nipple; phora: carrying) adj. With nipple-like protuberances. Syn. thelephoroid.

thelyotokous See thelytokous

thelyotoky See thelytoky.

Thelypteridaceae (Gr. thlypteris: female fern) n. A family of the phylum Filicinophyta.

thelytokous adj. Pertaining to or produced by thelytoky. Also thelyotokous.

thelytoky (Gr. thlytokia: parturition of female offsprings) n. The phenomenon occurring in the reproduction of certain animals in which fertilized eggs give rise to males and unfertilized eggs to females. It is found among aphids and certain other insects, and in some mites. The males are diploid, whereas females are haploid and transmit only the maternal genome - their production represents thelytokous parthenogenesis. Cf. arrhenotoky. Also thelyotoky.

theoid adj. Said of a leaf tooth in which the medial vein ends in an expanded and opaquely congested apex, no laterals are involved.

thermogenesis n. Generation or production of heat, especially by physiological processes.

thermogenetic adj. See thermogenesis. Also thermogenic.

thermogenic adj. See thermogenesis. Also thermogenetic.

thermoregulation n. The maintenance of a constant internal body temperature independent from the environmental temperature.

thermoregulatory adj. That concerns thermoregulation

therophyte (Gr. theros: season of warmth, of harvesting [summer]; phyton, a plant) n. An annual plant that dies after seed production and completes its entire life cycle within one year; it overwinters as a seed.

thicket n. A dense growth of shrubs or underbrush; a copse.

thigmotropic See thigmotropism.

thigmotropism n. The directional growth of a plant, in response to the stimulus of direct contact; the turning or bending response of an organism upon direct contact with a solid surface or object. This directional response is generally caused by the induction of some pattern of differential growth. This phenomenon is clearly illustrated by the climbing tendrils of some plants, such as the sweet pea. The tendrils actually 'feel' the solid object, which results in the coiling response. Also haptotropism, stereotropism.

thorn n. A stiff, woody, rigid process on a plant; specifically, a short, indurated, sharp-pointed, and leafless branch developed from a bud (replacing the growing point) in a manner typical to a leafy branch. In some plants the development of thorns and subsequent suppression of the growing points may be a response to dry conditions. Examples are the thorns of gorse and hawthorn. Sometimes applied to any structure resembling a true thorn. Cf. prickle, spine.

three-way cross A first generation hybrid between a single cross and an inbred line.

thrice compound See thrice-compound.

thrice-compound adj. Divided into leaflets that in turn are divided into leaflets, and then further divided into subleaflets.

throat n. The orifice of a gamopetalous corolla or gamosepalous calyx; the expanded portion of the corolla between the limb and the tube; the upper margin of the leaf sheath in grasses.

thrombophlebitis n. Inflammation of a vein with formation or presence of a thrombus and espcially one that is firmly attached to the vessel wall.

thrombosis n. The formation, development, or existence of a blood clot or thrombus within the vascular system.

thrum n. A heterostylic flower with a fairly short style and long stamens.

thujone n. A colourless liquid with a distinctive menthol odour, it is a ketone, a monoterpene, and is found in two stereoisomeric forms. It is found in certain plants such as arborvitae (genus Thuja, whence the derivation of the name), Nootka Cypress, some junipers, mugwort, sage, tansy and wormwood, usually as a mix of isomers. It is used as a flavouring agent in certain foods and is a compound in a number of other food additives. It is best known as a component of the drink absinthe, as it is a natural oil of wormwood (Artemisia absinthium). Although the compound is credited with hallucinogenic properties this is not certain. The chemical structure of thujone is loosely related to that of THC and it was formerly believed to have a similar structure-activity mechanism, but this has now been disproved. It is now believed that it antagonizes inhibition in the gamma-aminobutyric acid (GABA) receptor system. Its chemical formula is C10H16O.

thylakoid (Gr. thylakoeids: shaped like a sac, like a purse) n. Any of the flattened saclike membranous structures that are stacked on top of one another to form the grana (see granum) of plant chloroplasts. Chlorophyll and other photosynthetic pigments are situated in the thylakoid membranes, which are the site for the light reaction of photosynthesis (see also photophosphorylation). The photolysis of water (see photosystems) occurs in the space between the thylakoid membranes.

thyrse (Gr. thyrsos: thyrsus) n. A compact, cylindrical, or ovate panicle (branched inflorescence) with an indeterminate main axis and lateral branches determinate (cymose subaxes). Syn. thyrseus, thyrsus.

thyrseus See thyrse.

thyrsiform See thyrsoid.

thyrsoid (Gr. thyrsos: thyrsus; eid: to look like) adj. Thyrse-like. Also thyrsoidal, thyrsiform.

thyrsoidal See thyrsoid.

thyrsula (diminutive of Gr. thyrsos: thyrsus) n. A small cyme borne in the leaf axil, as in many members of the Labiatae (Lamiaceae).

thyrsus See thyrse.

tier n. A radial, layered branching habit of excurrent trees.

tiered adj. Having or arranged in tiers, rows, or layers, often used in combination, e.g. triple-tiered.

till n. Glacial drift consisting of an unassorted mixture of clay, sand, gravel, and boulders.

tiller n. A shoot that develops at the base of a plant stem from an axillary bud. Tillers are often produced in response to injury of the main stem, as occurs when a tree is lopped. Sprout, stalk, especially one from the base of a plant or from the axils of its lower leaves. A basal or subterranean shoot which is more or less erect. Cf. stolon, rhizome.

tillering n. A type of vegetative reproduction accomplished by tiller production.

tilosomes n. Masses of cellulosic and/or ligneous material in cells of the velamen next to the passage cells.

tissue n. A group of cells organized to perform a specific function, as epidermal tissue or vascular tissue.

tolerant (L. tolerans, tolerantis: withstanding) adj. Capable of growing without harm, in the shade, (shade tolerant), etc.

tomenta See tomentum.

tomentellous See tomentulose

tomentose (L. tomentum: that can be used as stuffing [wool, down, etc.]) adj. Densely covered with short, matted hair; bearing a tomentum. Covered with a thick felt of radicles.

tomentulose (diminutive of (L. tomentum: that can be used as stuffing [wool, etc.]) adj. Slightly tomentose. Also tomentose.

tomentum (L. tomentum: that can be used as stuffing) n. (pl. tomenta) A covering of dense, matted, woolly hairs, on stems and leaves; a felt-like covering of abundant rhizoids, e.g. the stems of Dicranum, Breutelia.

tongue n. Ligule.

tonic adj., n. An agent, such as a medication, that restores or increases body tone. Producing or stimulating physical, mental, or emotional vigor.

tonoplast n. The cytoplasmic membrane that surrounds a vacuole of a plant cell. Also vacuolar membrane.

tonsillitis n. An infection and swelling of the tonsils, which are oval-shaped masses of lymph gland tissue located on both sides of the back of the throat.

tooth n. Any small lobe or point along a margin.

toothed adj. Dentate.

topcross n. A cross between a selection, line, clone, etc., and a common pollen parent which may be a variety, inbred line, single cross, etc. The common pollen parent is called the top cross or tester parent. In corn, a top cross is commonly an inbred-variety cross.

topical adj. Of or applied to a localized area of the body or to the surface of a body part. Of or relating to a drug applied topically.

topically adv. See topical.

topotype A specimen of an organism taken from the type locality of that species, i.e. a pecimen of a plant collected from the same locality as the holotype and usually on a different date. A topotype has no formal standing.

tori See torus.

torose (L. torosus: knotty) adj. Cylindrical with alternate swellings and contractions.

tortuose See tortuous.

tortuous (L. tortuosus: winding, twisting) adj. Twisted or bent, irregularly; e.g. the leaves of Tortula when dry. Also tortuose.

torulose (diminutive of L. torosus: knotty) adj. Slightly torose, as in a small fruit which is constricted between the seeds.

torulous (L. torulus: small roll, small bulge) adj. Knotted; like moniliform, but with uneven bulges.

torus (L. torus: roll, bulge) n. (pl. tori). The receptacle of a flower. In lichens, a thickening or swelling around septa in certain thick-walled spores in Rinodina. See receptacle.

totipotency n. The ability of a cell, such as an egg, to give rise to unlike cells and thus to develop into or generate a new organism or part. Also totipotentiality.

totipotent adj. See totipotency.

totipotentiality n. The ability of a somatic cell to reproduce an entire plant somatically. Also totipotency.

Tournaisian n. 1. The earliest epoch in the Mississippian, preceded by the Famennian age (Devonian), followed by the Visean Epoch, and dated at 362.5 to 349.5 million years ago. It comprises the Hastarian and Ivorian Ages. 2. The name of the corresponding European/Russian series, which is roughly contemporaneous with the lower Carboniferous Limestone (Britain), and the Kinderhookian and lower Osagean (N. America). See also Dinantian.

toxicoses See toxicosis.

toxicosis n. (pl. toxicoses) A diseased condition resulting from poisoning.

trabecula (L. trabecula: small beam) n. (pl. trabeculae) A transverse partition dividing or partly dividing a cavity. A structure resembling a beam or crossbar. One of the projection from the cell wall which extends across the cell cavity of the ducts of certain plants, or the plate of cells across the cavity of the sporangium of a moss.

trabeculae See trabecula.

trabecular (L. trabecula: small beam) adj. Of or pertaining to trabeculae.

trabeculate (L. trabecula: small beam) adj. With a crossbar.

trace n. A vein

trace fossil A biogenic sedimentary structure formed by the behavioural activity of an animal on or within a given substrate. The study of trace fossils is called 'ichnology'. Traces are most frequent at the interface between different lithologies (e.g. sandstone and shale), and are classified on various criteria including morphology and preservation. Of these two, the second is preferred as a toponomic classification (i.e. classification by place of occurrence) and, apart from the processes of preservation, considers the position of the trace within the depositional unit concerned. In 1970, A. Martinsson divided traces into four groups dependent on their relationship to the casting medium: epichnia are surface ridges or grooves; endichnia are tubes or burrows formed within the casting medium; hypichnia are grooves or ridges preserved on the lower surface of the main body of the casting medium; and exichnia are formed by bioturbation outside the main body of the casting medium. See fossilization.

trachea (L. trachia: trachea) n. (pl. tracheae) Vessel.

tracheae See trachea.

tracheal (L. trachia: windpipe, trachea) adj. Of the nature of or composed of tracheae or vessels.

tracheary tissue General term for any water-conducting tissue such as the xylem, made up of tracheary elements, and water-conducting cells such as tracheids and vessel members.

tracheid (L. trachia: windpipe, trachea; eid: to look like) n. A type of cell occurring within the xylem of conifers, ferns, and related plants. Tracheids are elongated, slender, tapered at the ends, and their walls are usually extensively thickened by deposits of lignin. Water flows from one tracheid to another through unthickened regions (pits) in the cell walls.

Tracheophyta (L. trachia: windpipe, trachea; Gr. phyton: plant) n. A division of plants comprising green plants with a vascular system that contains tracheids or tracheary elements, being the Pteridophyta and Spermatophyta, commonly called vascular plants.

tracheophyte (L. trachia: windpipe, trachea; Gr. phyton: plant) n. Any plant that has elaborate tissues, including vascular tissue; a conspicuous sporophyte generation; and complex leaves with waterproof cuticles. Tracheophytes include plants of the phyla Psilophyta, Lycophyta, Sphenophyta, Filicinophyta, Coniferophyta, and Anthophyta. In traditional classification systems these were regarded as classes of the division Tracheophyta.

trachycarpous (Gr. trakhys: rough; karpos: fruit) adj. Rough-fruited.

trachyspermous (Gr. trakhys: rough; sperma: seed) adj. Rough-seeded.

trailing adj. Prostrate and creeping but not rooting.

trait n. A synonym of character with respect to function and performance.

trans- (L. trans: beyond, across, over) prefix. Meaning across, beyond, through

transcorrugated (L. trans: beyond, across, over; corrugatus: wrinkled) adj. Corrugated transversely to the axis.

trans-fatty acids See fatty acid.

transfer cells Metabolically active cells with labyrinthine inpushings of the walls, often found in association with vascular tissue or in seeds, apparently involved in the short-distance transfer of solutes.

transformational homology An an evolutionary series of character states with no significant breaks (from the plesiomorphic ancestor to the apomorphy in the descendant).

transfusion tissue Tissue made up of tracheids and parenchyma cells associated with a vascular bundle involved in the transfer of solutes.

transgressive segregation The appearance in the F2, or later generations of individuals, showing a more extreme development of character than either parent.

translator (L. translator: that carries elsewhere) n. The connecting structure between the pollinia of adjacent anthers in the Asclepiadaceae.

translocation n. The cHange in position of a segment of a chromosome to another part of the same chromosome or of a different chromosome.

translucent (L. translucere: to shine through) adj. Thin enough to pass light, but not an image; almost transparent. Also translucid.

translucid See translucent.

transpiration n. Emission of water vapor from the leaves, primarily through the stomata.

transversal See transverse.

transverse (L. transversus: oblique, transversal) adj. At a right angle to the longitudinal axis of a structure. Also transversal.

tree n. A woody plant at least 5 metres high, with a main axis the lower part of which is usually unbranched.

tri- (Gr. treis, tria, trion: three) prefix. Meaning three.

triachaenia See triachaenium.

triachaenium (Gr. treis, tria, trion: three; a-: without; khain: to open) n. (pl. triachaenia) A fruit consisting of three achenes.

triad (Gr. trias, triados; group of three) n. A group of three.

triadelphous (Gr. treis, tria, trion: three; adelph: sister) adj. With stamens arranged into three groups.

triandrous (Gr. treis, tria, trion: three; anr, andros: male) adj. With three stamens.

triangulate (L. tres, tria: three; angulus: angle) adj. Three-angled.

triarch adj. Cconsisting of three; for example a triarch stele has three lobes.

triaristate (L. tres, tria: three; arista: awn) adj. Three-awned.

Triassic n. The earliest (245 to 210 million years ago) of the three periods of the Mesozoic era. As a result of the mass extinctions of the late Palaeozoic, Triassic communities contained many new faunal and floral elements. Among these were the ammonites (Ammonoidea), modern corals, various molluscs (Mollusca), the dinosaurs, and certain gymnosperms.

tribe n. A category of taxa between subfamily and genus, grouping similar genera together.

tricarinate (L. tres, tria: three; carina: hull, keel) adj. With three ridges or keels.

tricarpellary (Gr. treis, tria, trion: three; karpos: fruit) adj. With three carpels.

trichasia See trichasium.

trichasial adj. With a trichasium.

trichasium (Gr. treis, tria, trion: three; kazo: separate) n. (pl. trichasia) A cymose inflorescence with three branches.

trichocarpous (Gr. thrix, trikhos: hair, bristle; karpos: fruit) adj. With hairy fruit.

trichogyne (Gr. thrix, trikhos: hair, bristle; gyn: female) n. A hailike prolongation of a carpogonium serving as a receptive organ for the spermatium. The receptive hypha of the female sexual organ.

trichogynial adj. See trichogyne.

trichogynic adj. See trichogyne.

trichome (Gr. trikhma: hair) n. A hair, scale, prickle, or other outgrowth from the epidermis of a plant. An outgrowth of the plant epidermis, either hairs or scales; a hair tuft; any hairlike outgrowth of the epidermis; in blue green algae, a single row of cells in a filamentous colony.

trichosclereid n. A long slender sclereid cell usually with branches.

trichotomous (formed on Gr. treis, tria, trion: three; and dikhotomos: cut in two) adj. Branching almost equally into three parts.

tricolpate adj. Describes pollen grains with three grooves or colpi.

tricolporate adj. Said of pollen grains, a common form having three vertically elongated apertures (colpi), each with a circular pore at the equator.

tricussate (formed on L. tres, tria: three; and decussate) adj. With whorls of three leaves, each alternating with leaves at the nodes above and below.

tricyclic (L. tres, tria: three; cyclicus: cyclic) adj. With three whorls as in a flower with calyx, gynoecium and androecium.

tridentate (L. tres, tria: three; dens, dentis: tooth) adj. Three-toothed.

tridenticulate adj. Minutely tridentate.

tridigitate (L. tres, tria: three; digitus: finger) adj. Divided into three finger-like lobes or divisions.

tridynamous (Gr. treis, tria, trion: three; dynamis: power) adj. With stamens arranged in two groups of three, one group often longer than the other.

triecious See trioecious.

trieciously adv. See triecious.

trifarious adj. Having three ranks of leaves. Cf. tristichous.

trifid (L. tres, tria: three; findere: to split) adj. Deeply divided into three parts or lobes, e.g. Tritomaria leaves. Three-cleft.

trifoliate (L. tres, tria: three; folia: leaf) adj. Having three leaves or three leaflets. Also trifoliated.

trifoliated See trifoliate.

trifoliolate (diminutive of L. tres, tria: three; folia: leaf) adj. Of a leaf, having three leaflets.

trifurcate (L. tres, tria: three; furca: fork) adj. Three-forked; divided in three branches.

trigamous (Gr. treis, tria, trion: three; gamos: marriage) adj. With three kinds of flowers, as in a plant with staminate, pistillate, and perfect flowers.

trigeminate (L. tres, tria: three; geminatus: doubled) adj. With three pairs of leaflets. Also trigeminous.

trigeminous (L. tres, tria: three; geminus: twin) See trigeminate.

trigonal (Gr. treis, tria, trion: three; gnia: angle) adj. Triangular in cross-section as applied to stems.

trigonous (Gr. treis, tria, trion: three; gnia: angle) adj. Trigonal; having three prominent longitudinal angles, as a style or ovary; triangular in cross-section and obtusely-angled. Cf. triquetrous.

trijugate (L. tres, tria: three; jugum: yoke) See trigeminate.

trilacunar adj. Said of nodal anatomy in angiosperms, where three leaf gaps are left in the central vascular cylinder when corresponding numbers of leaf traces depart.

trilete adj. Marking of the point for the germination of the prothallus; describing a spore with three laesurae, thus showing a trilete mark. Example: Pteridium (Hypolepidaceae). See spore.

trilobate (Gr. treis, tria, trion: three; lobos: lobe) adj. With three lobes. Also trilobed.

trilobed See trilobate.

Trilobita (Gr. treis, tria, trion: three; lobos: lobe) n. The most primitive arthropod class, known from more than 3900 fossil species. Inhabitants of Palaeozoic seas, the trilobites appeared first in the early Cambrian, had their widest distribution and greatest diversity in the Cambrian and Ordovician Periods, and became extinct in the Permian. The body was divided into three regions: an anterior cephalon, comprising at least five, fused segments; a mid-body or thorax, with a varying number of segments; and a hind region or pygidium. All three regions were divided by a pair of furrows running the length of the body, giving a trilobite appearance (i.e. a median or axial lobe, flanked on either side by a lateral lobe). The mouth was situated in the middle of the central surface of the cephalon. Paired gill-bearing limbs were attached to the membranaceous, pleural skeleton. X-ray studies show the eyes to have resembled the compound eyes of living arthropods (see Trilobite Eye). Trilobites ranged in size from 0.5 mm long planktonic (see Plankton) forms to those nearly 1 m in length; most species were 3 to 10 cm long. There were 9 orders: Redlichiida, Agnostida, Naraoiidae, Corynexochida, Lichida, Phacopida, Ptychopariida, Asaphida and Proetida.

trilobite n. Any marine arthropod of the extontc group Trilobita. See Trilobita.

trilocular (L. tres, tria: three; loculus: small box) adj. With three locules.

trimerous (Gr. treis, tria, trion: three; meros: part) adj. With parts arranged in sets or multiples of three. Composed of three or multiples of three; of a flower, having three segments in each perianth whorl and usually in each whorl of stamens also.

trimitic adj. Said of a fruiting body having three kinds of hyphae: generative (often with clamps), skeletal (often thick-walled) and binding hyphae (thin-walled).

trimonoecious (Gr. treis, tria, trion: three; monos: single; oikos: house) adj. With male, female, and bisexual flowers on the same plant, i.e. a plant having staminate, perfect, and pistillate flowers. Cf. androecious, andromonoecious, dioecious, gynoecious, gynomonoecious, hermaphroditic, monoecious.

trimorphic (Gr. treis, tria, trion: three; morph: shape) adj. With three forms. See trimorphism. Also trimorphous.

trimorphism (Gr. treis, tria, trion: three; morph: shape) n. The occurence of three different forms of flowers, leaves, etc., on the same plant, or on distinct plants of the same species.

trimorphous See trimorphic.

trinervate (L. tres, tria: three; nervus: tendon, ligament, nerve) See trinerved.

trinerved (L. tres, tria: three; nervus: tendon, ligament, nerve) adj. Three-nerved, with the nerves all arising from near the base. Cf. triplinerved. Also trinervate.

trinucleate adj. Said of pollen grains in which the male gametophyte has three nuclei when shed from the anther.

trioecious (Gr. treis, tria, trion: three; oikos: house) adj. With male, female, and bisexual flowers on different plants. Also triecious.

tripalmate (L. tres, tria: three; palmatus: stamped with the shape of a hand) adj. Palmately compound three times.

tripartite (L. tres, tria: three; pars, partis: part) adj. Three-parted.

tripetalous (Gr. treis, tria, trion: three; petalon: leaf) adj. With three petals.

triphyllous (Gr. treis, tria, trion: three; phyllon: leaf) adj. With three leaves.

tripinnate (L. tres, tria: three; pinnatus: feathered, winged) adj. Of leaves, thrice pinnately divided. Pinnately compound three times, with pinnate pinnules.

tripinnatifid (L. tres, tria: three; pinnatus: feathered; findere: to split) adj. When a pinnate leaf has leaflets that are pinnate, and those are also divided into pinna. Thrice pinnately cleft.

tripinnatisect adj. When a pinnatisect leaf has leaflets that are pinnatisect, and those are also divided into pinnatisect sections; tripinnatifid, but more deeply cut. See also tripinnatifid.

triple-nerved (L. triplus: triple; nervus: tendon, ligament, nerve) See triplinerved.

triplex See nulliplex.

triplicate adj. Folded three times.

triplinerved (L. triplus: triple; nervus: tendon, ligament, nerve) adj. Three-nerved, with the two lateral nerves arising from the midnerve above the base. Also triple-nerved.

triploid (Gr. tripls: triple; eidos: shape, appearance) n. Having or being a chromosome number three times the monoploid number. Describing a nucleus, cell, or organism that has three times (3n) the haploid number (n) of chromosomes (see also polyploid). Triploid organisms are normally sterile as their lack of homologous chromosomes prevents pairing during meiosis. This can be useful to plant breeders, for example in banana cultivation: sterile triploid bananas can be propagated asexually and will not contain any seeds.

tripterous (Gr. treis, tria, trion: three; pteron: wing) adj. With three wings or wing-like appendages.

triqueter (L. triquetrus: with three angles, triangular) adj. Three-edged. See triquetrous.

triquetrous (L. triquetrus: with three angles, triangular) adj. Three-edged; with three protruding angles. Triangular; having a triangular cross section acutely-angled; with three distinct longitudinal ridges. Cf. trigonous. Also triqueter.

trisepalous (Gr. treis, tria, trion: three; skepas: covering, shelter; [pe]talon: leaf) adj. With three sepals.

triseptate (L. tres, tria: three; septum: fence, partition) adj. With three septa.

triserial (L. tres, tria: three; seria: line, sequence) adj. Having only three verticils.

triseriate adj. In three rows; e.g. the leaves on a stem.

trisome See monosome.

trisomic adj., n. Of an otherwise diploid organism that has an extra chromosome of one pair (chromosome formula: 2n + 1).

trispermous (Gr. treis, tria, trion: three; sperma: seed) adj. Three-seeded.

tristichous (Gr. treis, tria, trion: three; stikhos: line, row) adj. Arranged in three vertical rows on a stem, each row in the same plane.

tristratose adj. In three layers.

tristylous (Gr. treis, tria, trion: three; stylos: column) adj. Of heterostylous species having three style lengths (short, mid, long), the flowers of any one plant having styles of the same length; having three styles.

trisulcate (L. tres, tria: three; sulcus: furrow) adj. With three furrows or grooves.

triternate (L. tres, tria: three; terniL by three) adj. Triply ternate.

triterpene See triterpenes.

triterpenes n. pl. A terpene with 6 isoprene units. See terpenes.

trochlear See trochlearate.

trochlearate (L. trochlea: pulley) adj. Pulley-shaped; in the form of a pinched circle resembling a figure of eight. Also trochlear, trochleariform.

trochleariform (L. trochlea: pulley; forma: shape) See trochlearate.

trophic adj. Of or relating to nutrition. Of or involving the feeding habits or food relationship of different organisms in a food chain.

trophic level A group of organisms that derive their energy from the same part of the food chain. An example of this is herbivores, which feed on plants.

tropical (L. tropicus: tropical) adj. Distributed in the tropics (i.e. between the tropic of Cancer and the tropic of Capricorn).

tropism n. The movement of an organism in response to an external source of stimulus, usually toward or away from it, including aerotropism, geotropism, haptotropism, hydrotropism, phototropism, and thigmotropism.

trullate adj. With the widest axis below the middle and with straight margins; ovate but margins straight and angled below middle, trowel-shaped.

trulliform adj. Shaped like a bricklayer's trowel, i.e. broadest below the middle, rhombic, with the two lower equal sides equal and shorter than the two equal upper sides.

truncate (L. truncatus: cut down, shortened, amputated) adj. Terminating abruptly, as if tapering end were cut off; cut squarely across, either at the base or apex of an organ.

trunk (L. truncus: trunk, stump) n. The main stem of a tree below the branches.

tryma n. (pl. trymata) A drupe-like nut with a fleshy, dehiscent exocarp, as a walnut or hickory nut.

trymata See tryma.

tryptophan n. An essential amino acid, formed from proteins during digestion by the action of proteolytic enzymes. It is necessary for normal growth and development and is the precursor of several substances, including serotonin and niacin.

tubate (L. tuba: trumpet, pipe) adj. Having or forming a tube or tubes,; tubular; trumpet-shaped.

tube (L. tuba: pipe) n. A hollow, cylindrical structure, as the constricted basal portion of some gamopetalous corollas

tube flower A Floret with a tubular corolla, usually five-lobed.

tuber (L. tuber: bump, outgrowth) n. A swollen underground stem or root in certain plants. It enables the plant to survive the winter or dry season and is also a means of propagation. A stem tuber, such as the potato, forms at the end of an underground stem. Each tuber represents several nodes and internodes. The following season several new plants develop from the terminal and axillary buds (eyes). Root tubers, such as those of the dahlia, are modified food-storing adventitious roots and may also give rise to new plants. In liverworts, geotropic outgrowth from the shoot apex, composed of perennating tissue, allowing for aestivation and subsequent continued growth or vegetative reproduction; e.g. Petalophyllum; in mosses, gemmae born on rhizoids (rhizoidal gemmae), found in many acrocarpous mosses; e.g. Bryum.

tubercle (L. tuberculum: small bump; small outgrowth) n. A small rounded protuberance, root swelling or nodule; a thickened, solid, spongy crown or cap, as on an achene; a small tuber or tuberlike growth; an underground stem which has been modified for storage of nutrients, such as a potato; the base of the style in some members of the Cyperaceae. Also tuberculum.

tubercula See tuberculum.

tubercular (L. tuberculum: small bump, small outgrowth) adj. Of, pertaining to, or of the nature of tubercle or tubercles; characterized by or having tubercle. Also tuberculate.

tubercularly See tubercular.

tuberculate (L. tuberculum: small bump, small outgrowth) adj. Covered with tubercles; tubercular.

tuberculated See tuberculate.

tubercule n. A nodule, as on the roots of some legumes.

tuberculose See tuberculate.

tuberculostatic adj. Inhibiting the growth of Mycobacterium tuberculosis, the tuberculosis bacillus.

tuberculum n. (pl. tuberculua) Tubercle.

tuberiferous (L. tuber: bump, outgrowth; ferre: to carry) See tuberculate.

tuberiform (L. tuber: bump, outgrowth; forma: shape) adj. Resembling a tuber.

tuberoid (L. tuber: bump, outgrowth; Gr. eid: yo look like) adj. A thickened root which resembles a tuber.

tuberose See tuberous.

tuberous (L. tuberosus: filled with protuberances, with bumps adj. Swollen; characterized by the presence of wartlike prominences or tubers; of roots, tuber-like; producing, bearing tubers. Also tuberose.

tubular (L. tubulus: small pipe) adj. With the form of a tube or cylinder.

tubuliflorous (L. tubulus: small pipe; florus: flowered)) adj. Having tubular corollas in the perfect flowers of a head, as in some members of the Compositae (Asteraceae).

tubulin n. A globular protein that polymerizes to form microtubules. The major protein component of microtubules, which is formed of two different monomers (tubulin A and tubulin B).

tubulose (L. tubulus: small pipe) adj. Consisting of, or resemblinng, small tubes; referring to leaves with strongly incurved or broadly overlapping leaf margins; e.g. Campylopus.

tubulous (L. tubulus: small pipe) adj. With tubular flowers.

tufted adj. Arranged in a dense cluster.

tumescence n. See tumescent.

tumescent (L. tumescere: to swell) adj. Somewhat tumid; swelling.

tumid (L. tumidus: swollen) adj. Swollen; inflated. Syn. intumescent.

tundra n. A vast treeless plain in the arctic regions between the ice cap and the tree line.

tunic (L. tunica: any kind of covering) n. The thin membranous or fibrous outer layers of a bulb or corm; a natural integument; the outer coating of a seed or bulb.

tunicate (L. tunica: any kind of covering) adj. Arranged in sheathing, concentric layers, as the leaves of an onion bulb.

turbinate (L. turbinatus: of a conical shape) adj. Inversely conical; obconical; shaped like a cone resting on its apex.

turgent adj. Swelling; swollen, turgid. Also turgescent.

turgescent (L. turgescere: to swell) adj. Becoming swollen; swelling. Also turgent.

turgid adj. Swollen due to high water content. Cf. flaccid. Also turgent.

turgor (L. turgor: swelling) n. A condition in a plant cell in which the cell has taken up water so that the plasma membrane exerts an equal and opposite force to that exerted by the surrounding cell wall. Turgor is important in support, and plants which lose turgor start to wilt.

turgor pressure Force exerted outward on a cell wall by the water contained in the cell. This force gives the plant rigidity, and may help to keep it erect.

turion (L. turio, turionis: young shoot) n. A winter bud, covered with scale leaves and mucilage, that is produced by certain aquatic plants, such as frogbit. Turions become detached and remain dormant on the pond or lake bottom during the winter before developing into new plants the following season. A small shoot which often over winters, as in Asparagus and in some species of Epilobium.

tussock n. A tuft or clump of grasses or sedges.

twice compound See twice-compound.

twice-compound With the leaflets again divided into leaflets.

twig n. A small shoot or branch from a tree.

twining adj. Coiling or spiraling around a support (usually another stem) for climbing. Winding around something; twisting; embracing.

two-ranked adj. In two vertical ranks or rows on opposite sides of an axis; distichous.

tylose See tylosis.

tylosis n. (pl. tyloses) The outgrowth from adjacent parenchymatous cells through a pit cavity in a vessel wall, more or less blocking the lumen. Also tylose.

type (Gr. typos: mark, image) n. One of several categories of herbarium specimens, chosen by taxonomists as being close or identical to that chosen by the original author. A designated representative of a plant name.

type genus The taxonomic genus that is designated as representative of the family to which it belongs.

type species A type that fixes a name to a taxon. Depending on the Code which is applied to the organism in question, a type may be a specimen, culture, illustration, description or taxon. Also type specimen.