Vitex L.

Scientific Description

Common name. Vitex. Family Verbenaceae.

Habit and leaf form. Shrubs, or trees; evergreen, or deciduous; bearing essential oils. Plants unarmed. Leaves cauline. Young stems cylindrical, or tetragonal (obscurely). To 0.1–20 m high. Leptocaul. Leaves small to medium-sized; not fasciculate; opposite; decussate; ‘herbaceous’; not imbricate; petiolate to subsessile; aromatic, or without marked odour, or foetid; simple, or compound; epulvinate; unifoliolate, or ternate, or palmate. Lateral leaflets opposite. Leaflets epulvinate; ovate (or broadly so), or elliptic, or ovate, or obovate, or orbicular; cuneate at the base; flat. Leaflet margins flat. Leaf blades entire; flat; broadly elliptic, or elliptic; pinnately veined, or palmately veined; cross-venulate. Mature leaf blades adaxially glabrous, or pubescent; abaxially glabrous, or woolly (greyish velutinous or silky). Leaves without stipules. Leaf blade margins entire; flat. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present. Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence many-flowered. Flowers in cymes. The terminal inflorescence unit cymose. Inflorescences terminal, or axillary; cymose, compound and often much branched, terminal or axillary, usually pedunculate. Flowers pedicellate, or subsessile; bracteate; bracteolate. Bracteoles not adnate to the receptacle. Flowers small to medium-sized; very irregular; zygomorphic. The floral asymmetry involving the perianth and involving the androecium. Flowers 4–5 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present, or absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; entire, or lobed; lobulate, or blunt-lobed, or toothed; prominently 5 veined; erect; open in bud; exceeded by the corolla; cupuliform, or cyathiform (and tubular below), or campanulate (or more or less); regular; greyish green, or green (pale to dark); persistent; accrescent, or non-accrescent; with the median member posterior. Corolla present; 5; 1 -whorled; gamopetalous; lobed; blunt-lobed; imbricate; tubular, or funnel-shaped; unequal but not bilabiate to bilabiate; hairy abaxially (pubescent and sometimes glandular); hairy adaxially (densely villous in parts, remainder glabrous); with contrasting markings; purple, or violet, or blue, or white to cream (rarely), or white (some with a purple lip); deciduous; non-accrescent. Corolla lobes broadly or more or less ovate, or orbicular, or elliptic to oblong, or obovate. Corolla members entire. Androecium present. Androecial members definite in number. Androecium 4. Androecial sequence not determinable. Androecial members adnate (to the corolla tube); markedly unequal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 4. Staminal insertion midway down the corolla tube. Stamens becoming exserted; didynamous; all more or less similar in shape; reduced in number relative to the adjacent perianth; fertile stamens representing the posterior-lateral pair and the anterior-lateral pair; oppositisepalous. Filaments hairy; filiform. Anthers connivent, or separate from one another; dorsifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate. Gynoecium 2 carpelled. The pistil 4 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 2 locular. Locules secondarily divided by ‘false septa’. Gynoecium median. Ovary sessile. Ovary summit glabrous, or hairy, the hairs not confined to radiating bands (at the ovary apex). Gynoecium stylate. Styles 1; simple; attenuate from the ovary; apical; much longer than the ovary at anthesis; becoming exserted; hairless. Stigmas 1; 2 - lobed. Placentation axile. Ovules 2 per locule (one per cell); pendulous, or horizontal, or ascending; non-arillate; hemianatropous.

Fruit and seed features. Fruit 3–13 mm long; fleshy; indehiscent; a drupe; 4 celled; 2 locular. Seeds non-endospermic. Cotyledons 2 (expanded, flat). Embryo straight.

Special features. Calyx limb 5 lobed. Corolla tube exceeding the calyx; straight. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla bilobed; upper (adaxial) lip of the corolla not concave. Lower (abaxial) lip of the corolla 3 lobed; not concave. Stamens projecting straight forwards or spreading.

Geography, cytology, number of species. Native of Australia. Endemic to Australia and not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, Queensland, and New South Wales. Northern Botanical Province. A genus of ca 250 species; 5 species in Western Australia; 1 endemic to Western Australia.

Etymology. From the Latin vitex; name used by Pliny for the chaste tree, or Abraham's balm, V. agnus-castus.