Common name. Basil. Family Lamiaceae.
Habit and leaf form. Shrubs (or undershrubs), or herbs; evergreen; bearing essential oils. Plants unarmed. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Young stems usually tetragonal. To 0.1–1 m high. Leaves medium-sized; not fasciculate; opposite; not decurrent on the stems; membranous; not imbricate; petiolate; aromatic; simple; epulvinate. Leaf blades entire; flat; narrowly ovate, or ovate to elliptic; pinnately veined; cross-venulate; attenuate at the base, or cuneate at the base. Mature leaf blades adaxially pubescent (to sparsely), or glabrous (to glabrescent); abaxially pubescent (to sparsely), or glabrous (to glabrescent). Leaves without stipules. Leaf blade margins entire; flat. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; glandular hairs present. Urticating hairs absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous, or ornithophilous; usually via hymenoptera, or via lepidoptera, or via diptera.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence few-flowered. Flowers in verticils. The terminal inflorescence unit cymose. Inflorescences axillary; with units (2)3-flowered. Flowers pedicellate (recurved); bracteate; ebracteolate; small; fragrant (strongly aromatic plants, lemon-scented in Australian species); somewhat irregular to very irregular; zygomorphic; cyclic; tetracyclic. Floral receptacle developing a gynophore, or with neither androphore nor gynophore. Free hypanthium absent. Perianth with distinct calyx and corolla; 4–10; 2 -whorled; isomerous, or anisomerous. Calyx present; 5; 1 -whorled; gamosepalous; blunt-lobed, or toothed (unequally 5-lobed, the 2 abaxial and 2 lateral lobes subequal and much narrower than the single adaxial lobe); imbricate, or open in bud; tubular- campanulate; bilabiate; non-fleshy; persistent (enlarging in fruit); non-accrescent; with the median member posterior. Corolla present; disguisedly 5; 1 -whorled; gamopetalous; blunt-lobed; imbricate; campanulate; bilabiate (‘abaxial lobe narrow basally, lateral and adaxial lobes subequal’); with contrasting markings; white, or purple (mauve), or pink (pinkish to mauve). Corolla lobes broad obovate to ovate (broadly, distally). Corolla members entire. Androecium present. Fertile stamens present, or absent. Androecial members definite in number. Androecium 4. Androecial members adnate; markedly unequal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 4. Staminal insertion near the base of the corolla tube (the posterior pair), or in the throat of the corolla tube (the anterior pair). Stamens inserted at markedly different levels; 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 (abaxial pair inserted in corolla mouth, adaxial pair near base of corolla tube); all alternating with the corolla members. Filaments appendiculate (with a hairy appendage — actually a sterile anther cell — near the base); glabrous (except the hairy appendage); filiform. Anthers connivent, or separate from one another; dorsifixed; versatile, or non-versatile; dehiscing via longitudinal slits; introrse; unilocular; tetrasporangiate; appendaged, or unappendaged. Pollen shed as single grains. Fertile gynoecium present, or absent. Gynoecium 2 carpelled (the carpels deeply lobed to mimic G4). The pistil 4 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 2 locular (originally), or 4 locular (by intrusions of the ovary wall constituting ‘ false septa’). Locules secondarily divided by ‘false septa’. Gynoecium median; stylate. Styles 1; simple; from a depression at the top of the ovary (the ovary deeply lobed); ‘gynobasic’; becoming exserted. Stigmas 2; 2 - lobed. Placentation basal. Ovules 2 per locule, or 1 per locule (two per original loculus, but one per locellus); ascending; apotropous; non-arillate; anatropous, or hemianatropous.
Fruit and seed features. Fruit non-fleshy; a schizocarp. Mericarps (2–)4; comprising nutlets. Seeds endospermic to non-endospermic. Embryo well differentiated. Cotyledons 2. Embryo straight.
Special features. The flowering nodes separated by extended internodes. (2–)3(–4) flowers subtended by each floral leaf. Calyx limb 5 lobed. Corolla tube usually not exceeding the calyx. The upper lip of the corolla incorporating 4 members, the lower 1; (posterior, adaxial) lip of the corolla 4 lobed. Lower (abaxial) lip of the corolla markedly concave. Stamens descending.
Geography, cytology, number of species. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. Northern Botanical Province. A genus of 6 species; 2 species in Western Australia; 0 endemic to Western Australia.
Etymology. Name used by Pliny for the plant basil, O. basilicum, said to be from the Greek for "to smell" on account of the powerful scent of the plants.