Lavandula L.

Scientific Description

Common name. Lavenders. Family Lamiaceae.

Habit and leaf form. Shrubs, or herbs; bearing essential oils. Plants unarmed. Perennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Young stems tetragonal. To 0.3–1 m high. Leptocaul. Leaves small to medium-sized; fasciculate; opposite, or opposite to whorled (clustered at the nodes); not decurrent on the stems; ‘herbaceous’; imbricate, or not imbricate; sessile; aromatic; simple; epulvinate. Leaf blades dissected, or entire; rolled; linear, or oblong (narrowly); pinnatifid; pinnately veined; cross-venulate; cordate to cuneate at the base, or rounded at the base. Mature leaf blades adaxially scabrous; abaxially greyish woolly. Leaves without stipules. Leaf blade margins entire; revolute. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; glandular hairs present; complex hairs present. Branched hairs absent. Complex hairs stellate. Urticating hairs absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present (flowers produce much nectar). 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 terminal; of loose or dense, pedunculate, cylindrical, terminal spikes, with 2–10-flowered verticillasters. Flowers pedicellate; bracteate; bracteolate. Bracteoles not adnate to the receptacle. Flowers small; somewhat 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 (the uppermost often appendaged); prominently 8–15 veined; imbricate, or open in bud; exceeded by the corolla; tubular; regular to bilabiate; non-fleshy; persistent; with the median member posterior. Calyx lobes oblong, or orbicular (lobes short, the uppermost lobe often with an appendage). Corolla present; more or less disguisedly 5; 1 -whorled; gamopetalous; blunt-lobed; imbricate; bilabiate (with the upper lip 2-lobed and the lower 3-lobed), or regular (sometimes scarcely 2-lipped, and with 5 almost equal lobes); plain, or with contrasting markings; dark purple, or white (rarely), or pink (rarely). Corolla lobes orbicular. Corolla members entire. Androecium present. Fertile stamens present. 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 midway down the corolla tube, or in the throat of 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; all alternating with the corolla members. Filaments filiform. Anthers connivent, or separate from one another; dorsifixed; versatile, or non-versatile; dehiscing via longitudinal slits; introrse; unilocular; tetrasporangiate; unappendaged. Pollen shed as single grains. Fertile gynoecium present. 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’. Stigmas 2. 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, or 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 aggregated in dense heads, or aggregated in dense spicate inflorescences. 1–5 flowers subtended by each floral leaf. Calyx limb 5 lobed. Corolla tube exceeding the calyx; straight to curved. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla bilobed. Lower (abaxial) lip of the corolla 3 lobed. Stamens projecting straight forwards or spreading. The anterior pair of stamens exceeding the posterior pair.

Geography, cytology, number of species. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, New South Wales, and Victoria. A genus of ca 28 species; 3 species in Western Australia; 0 endemic to Western Australia.

Etymology. From the Latin lavandula or livendula, the lavender plant, perhaps from the Latin for "blue, bluish", or "to wash".