Verbena L.

Scientific Description

Common name. Verbenas. Family Verbenaceae.

Habit and leaf form. Herbs; evergreen; bearing essential oils. Plants unarmed. Annual to perennial. Leaves basal. Young stems tetragonal. To 0.5–0.8 m high. Leaves medium-sized; not fasciculate; opposite (usually), or whorled; usually decussate; occasionally 3 per whorl; ‘herbaceous’; not imbricate; sessile; aromatic, or without marked odour, or foetid; simple; epulvinate. Leaf blades entire; flat; narrowly oblong, or ovate, or elliptic; pinnately veined; cross-venulate; somewhat amplexicaul. Mature leaf blades adaxially glabrous, or scabrous, or villous; abaxially scabrous, or woolly. Leaves without stipules. Leaf blade margins dentate; flat. Leaves without a persistent basal meristem. 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 spikes, or in panicles, or in cymes. The terminal inflorescence unit racemose. Inflorescences terminal; a spike or a terminal panicle or corymb of elongate spikes. Flowers subsessile, or sessile; bracteate; small; 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; (9–)10; 2 -whorled; isomerous to anisomerous. Calyx present; 4, or 5; 1 -whorled; gamosepalous; lobed; toothed; prominently 4–5 veined (ribbed); erect; exceeded by the corolla; usually tubular; unequal but not bilabiate; persistent; with the median member posterior. Corolla present; 5; 1 -whorled; gamopetalous; lobed; blunt-lobed. Corolla lobes markedly shorter than the tube. Corolla imbricate; hypocrateriform and tubular; bilabiate; hairy adaxially (with soft hairs inside throat and tube); blue, or red to purple. Corolla lobes broadly ovate, or orbicular. 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 remaining included; 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. 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. Gynoecium stylate. Styles 1; simple; attenuate from the ovary; apical; much longer than the ovary at anthesis; not becoming exserted. Stigmas 1; unequally 2 - lobed. Placentation basal to axile. Ovules 2 per locule (one per cell); ascending; non-arillate; anatropous.

Fruit and seed features. Fruit non-fleshy; a schizocarp. Mericarps 4; comprising nutlets. Endocarp ribbed. Fruit 4 seeded. Seeds 1 per mericarp. Seeds non-endospermic; small. Cotyledons 2 (expanded, flat). Embryo straight.

Special features. Calyx limb 4 lobed, or 5 lobed. Corolla tube exceeding the calyx; straight, or curved. 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.

Geography, cytology, number of species. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. South-West Botanical Province. A genus of ca 250 species; 2 species in Western Australia; 0 endemic to Western Australia.

Etymology. From the Latin verbena; used in the plural verbenae for the leaves or twigs of plants used for sacred purposes, usually vervain, V. officinalis. The name was adopted for the plant in modern literature by Brunfels in 1530, and is said to be adapted from Italian or Spanish.