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.

urceolate: urn-shaped.

utricle: a small bladder; a membranous bladder-like sac enclosing an ovary or fruit.

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Last updated on 13 May 1999.

Australian Biological Resources Study