tannin: a complex, aromatic compound occurring in the bark of many shrubs and trees.
tanniniferous: producing tannins.
taproot: the main, descending root of a plant that has a single, dominant root axis.
taxon: a group or category, at any level, in a system for classifying plants or animals. pl. taxa.
tendril: a slender climbing organ formed by modification of a part of a plant, e.g. a stem, a leaf or leaflet, a stipule.
tenuiexinous: of a pollen grain, with a thin exine.
tepal: a perianth segment in a flower in which all the perianth segments are similar in appearance.
terete: cylindrical or nearly so; circular in cross-section.
terminal: at the apex or distal end.
ternate: in groups of three; of leaves, arranged in whorls of three; of a single leaf, having the leaflets arranged in groups of three.
ternatifid: of leaves, deeply cut into three lobes. cf. pinnatifid.
terrestrial: of or on the ground; of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.
testa: a seed coat.
tetrad: a group of four; four pollen grains remaining fused together at maturity, e.g. in Ericaceae, Epacridaceae.
tetradynamous: of an androecium, consisting of four stamens of the same length and two of a different length. cf. didynamous.
tetramerous: of a flower, having four segments in each perianth whorl, and usually four in each whorl of stamens also.
thallus: the vegetative body of a plant that is not differentiated into organs such as stems and leaves, e.g. the gametophytes of ferns, and Lemnaceae.
thigmotaxis: a response, by movement or growth, to a mechanical stimulus, e.g. the leaves of 'Sensitive Plant' (Mimosa), the leaf hairs of Drosera, or the tendrils of many climbing plants. adj. thigmotactic.
thorn: a modified plant organ, especially a stem, that is stiffened and terminates in a pungent point.
throat: of a corolla tube, the top, where the tube joins the lobes.
thyrse: a branched inflorescence in which the main axis is indeterminate and the lateral branches determinate in their growth.
tomentellous: minutely tomentose.
tomentum: a covering of dense, matted, woolly hairs. adj. tomentose.
torus: see receptacle.
trabecula: a transverse partition dividing or partly dividing a cavity.
translator: applied to parts of a pollinarium, comprising the central part or corpusculum, and the arm-like structures or caudicles uniting the corpusculum with the pollinia.
trapeziform: having four straight unequal sides.
tree: a woody plant at least 5 metres high, with a main axis the lower part of which is usually unbranched.
trichome: an epidermal outgrowth, e.g. a hair (branched or unbranched), a papilla.
trichotomous: branching almost equally into three parts.
trifid: deeply divided into three parts.
trifoliate: having three leaves.
trifoliolate: of a leaf, having three leaflets.
trigonous: triangular in cross-section and obtusely-angled. cf. triquetrous.
trimerous: of a flower, having three segments in each perianth whorl and usually three in each whorl of stamens also.
tripartite: divided into three parts.
tripinnate: of leaves, thrice pinnately divided. cf. bipinnate, pinnate.
triplicate: folded three times.
triquetrous: triangular in cross-section and acutely-angled; with three distinct longitudinal ridges. cf. trigonous.
tristichous: arranged in three rows on a stem, each row in the same plane.
tristylous: heterostylous species having three style lengths (short, mid, long), the flowers of any one plant having styles of the same length.
trulliform: shaped like a bricklayer's trowel, i.e. angular-ovate, broadest below the middle, rhomboid with the two lower equal sides shorter than the upper.
truncate: with an abruptly transverse end, as if cut off.
tuber: a storage organ formed by swelling of an underground stem or the distal end of a root.
tubercle: a small wart-like outgrowth.
tuberculate: covered with tubercles.
tuberous: swollen; of roots, tuber-like.
tumid: swollen; inflated.
tunic: of a bulb or corm, the thin membranous or fibrous outer layers.
turbinate: top-shaped, obconical.
turgid: swollen due to high water content. cf. flaccid.
turion: an over-wintering vegetative bud or specialised short shoot with modified leaves, arising from the stem, often near ground level.
type: a designated representative (standard) for a plant name. cf. holotype, isotype, lectotype, neotype, paratype, syntype.
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umbel: a racemose inflorescence in which all the individual flower stalks arise in a cluster at the top of the peduncle and are of about equal length.
umbellule: secondary umbel in a compound umbellate inflorescence.
uncinate: terminating in a hooked point.
undulate: wavy, i.e. not flat. cf. sinuate.
unifacial: of leaves, where the adaxial (upper) edge is homologous with the adaxial surface of a dorsiventral leaf and the remainder is derived from the abaxial surface. cf. bifacial.
unifoliate: having one leaf.
unifoliolate: of a leaf, basically compound, but reduced to only one leaflet.
unilateral: of stamens, with anthers grouped on one side of the style.
unilocular: of an ovary, anther or fruit, having only one internal cavity.
unisexual: bearing only male or only female reproductive organs.
united: fused together.
utricle: a small bladder; a membranous bladder-like sac enclosing an ovary or fruit.
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Last updated on 13 May 1999.