taproot: the main, descending root of a plant that has a single, dominant root system.

taxon: a term used to describe a member of any taxonomic category, e.g. genus, species. pl. taxa.

taxonomy: the study of the principles and practices of classification, the establishing and defining of relationships; often used interchangeably with systematics, but strictly taxonomy is only part of systematics.

tendril: a long slender, coiled organ derived from an axis or leaf, or from part of one of these.

tepal: a free segment of a perianth that is not differentiated into a calyx and corolla.

terete: cylindric and elongated. Fig. 10 H.

terminal: at the apex.

terminal petiolule: the stalk of the terminal leaflet of a pinnately 3-foliolate leaf or an imparipinnate leaf; the stalk is usually jointed at the point where the rachis extension beyond the last leaflet meets the true petiolule of the leaflet. Fig. 3 C & K.

ternate: in threes, e.g. of a single leaf, having the leaflets arranged in groups of three. Fig. 3 K & L. cf. biternate.

terrestrial: of the land as opposed to living in water. cf. aquatic.

tessellated: with colours or shapes arranged in squares to give a chequered appearance, e.g. of bark.

testa: the seed coat.

tetrad: a group of four; as in four pollen grains remaining together at maturity in Ericaceae subfamily Styphelioideae.

tetradynamous: of an androecium, consisting of four stames of the same length and two of a different length; as in many Brassicaceae.

tetramerous: of a flower, having four segments in each perianth whorl, and usually in each whorl of stamens also.

tetrasporangiate (4-sporangiate): of an anther in which there are 4 pollen sacs (sites of pollen grain formation or microsporangia). cf. unisporangiate.

thallus: the vegetative body of a plant that is not differentiated into organs such as stems and leaves, e.g. algae, the gametophytes of many liverworts, and family Lemnaceae.

thorn (spine): a stiff process with a sharp point, formed by a modification of a plant organ that contains vascular tissue, e.g. a lateral branch or a stipule. cf. prickle.

throat: of a corolla tube or hypanthium, the top where the tube joins the lobes.

thyrse: a compound inflorescence ending in a vegetative (non-floral) bud and with mixed types of branching, the main axis bearing several or many lateral cymes. Fig. 17 C.

thyrsoid: a compound inflorescence which ends in a flower and in which the main axis is raceme-like and the lateral ones cymose, i.e. similar to a thyrse except for the terminal flower. Fig. 17 B.

tiller: the shoot of a grass, usually lateral and basal and more or less erect.

tomentellous: minutely tomentose.

tomentose: covered with dense intertwined hairs. Fig. 14 E. n. tomentum. cf. woolly.

tomentum: a dense covering of intertwined hairs. Fig. 14 E. adj. tomentose.

toothed: of margins, regularly or irregularly incised. Fig. 8 C.

torus: see receptacle.

trabeculate: cross-barred.

tree: a woody plant usually with a single distinct trunk and generally more than 5 m high.

tri-: a prefix: in threes, as in: trifoliolate, having three leaflets; trimerous, with flower parts arranged in threes.

triad: a three-flowered inflorescence of dichasial form. Fig. 17 F.

triangular: a 2-dimensional shape, 3-angled and 3-sided. Fig. 5 K.

tribe: a taxonomic grouping, in rank between family and genus.

trichome: a hair, bristle, scale or other such outgrowth of the epidermis. Fig. 14 & Fig. 15.

trichotomous: branching almost equally into three parts.

trifid: deeply divided into three parts.

trifoliate: having three leaves. cf. trifoliolate.

trifoliolate: of a leaf, having three leaflets. Fig. 3 K & L. See also palmately trifoliolate, pinnately trifoliolate.

trigonous: triangular in cross-section and with the angles somewhat rounded. Fig. 10 F. cf. triquetrous.

trimerous: of a flower, having three segments in each perianth whorl and usually in each whorl of stamens also.

trimorphic: occurring in three different forms. cf. dimorphic.

tripinnate (3-pinnate): of a compound leaf, with lamina pinnately divided three times, i.e. the pinnules are again pinnately divided. Fig. 3 A. cf. bipinnate.

triplicate: folded three times.

triquetrous: triangular in cross-section and sharply angled; with three distinct longitudinal ridges. Fig. 10 G. cf. trigonous.

tristylous: heterostylous species with styles of 3 different lengths (short, mid, long).

trullate: ovate, but angled; like a brick-layer’s trowel; inverse kiteshaped.

truncate: with an abruptly transverse edge as if cut off, e.g. of a lamina apex (Fig. 6 F), or base (Fig. 7 D).

tuber: an underground storage organ formed by the swelling of a stem, e.g. a potato. adj. tuberous.

tubercle: a small wart-like outgrowth, e.g. forming the base of a hair.

tuberculate (warty): having the surface rough with tubercles or small wart-like outgrowths. Fig. 16 C.

tuberoid: a storage organ which is a tuber-like thickening of a root (and generally bears no lateral eyes) as in many terrestrial orchids.

tuberous: swollen; of roots tuber-like.

tumid: swollen; inflated.

tunicate: with coats or tunics; as in bulbs or corms covered with a thin membranous or fibrous outer layers.

turbinate: top-shaped.

turgid: swollen owing to high water content.

turion: a specialized dwarf shoot with modified leaves, and formed by some species in winter. Turions mostly fall from the parent plant, remain dormant over winter, and then sprout to form new individuals.

tussock: a large clump or tuft, usually of a perennial herb, especially grasses.

two-ranked (2-ranked): arranged in two rows on opposite sides of a stem and in the same plane. Fig. 2 B.

type: the designated representative of a taxon constituting a fixed point for the application of its name, for determining priority of usage.

umbel: an inflorescence (strictly an indeterminate one) in which all the flowers or flower-stalks arise from one point at the top of the peduncle. Fig. 17 J. adj. umbellate. cf. umbelliform.

umbellaster: a group of flowers (with the terminal bud ending in a flower) more or less arising from the one point, which may be derived from the condensation of a cyme, thyrsoid or panicle.

umbelliform (umbelloid): having the form of an umbel.

umbo: a conical projection arising from the surface. adj. umbonate.

unarmed: without spines or prickles.

uncinate: terminating in a hooked point.

undershrub: a small shrub, often partially herbaceous.

undulate: wavy, i.e. not flat. Fig. 8 J. cf. sinuate.

uni-: prefix: one: as in unisexual, of flowers with one sex.

uniflorescence: a unit inflorescence forming part of a conflorescence.

unifoliolate leaf (1-foliolate): a compound leaf reduced to a single leaflet, usually recognized by the articulated or jointed ‘petiole’, which is in fact a petiole plus a petiolule. Fig. 3 K.

unigeneric: of a family, having only one genus. cf. monotypic.

unilateral: of stamens, with anthers grouped to one side of the style.

unilocular: of an ovary, anther or fruit, having only one internal cavity.

unisexual: bearing only male or female reproductive organs, not both. cf. dioecious, monoecious.

unisporangiate (1-sporangiate): of an anther with only 1 pollen sac (area of pollen grain formation, microsporangium). cf. tetrasporangiate.

united: fused together.

unitubulose: organs with complete transverse septa and no obvious longitudinal septa (seen by splitting the organ). cf. pluritubulose.

urceolate: urn-shaped.

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