Lamium L.

Scientific Description

Family Lamiaceae.

Habit and leaf form. Herbs; evergreen; bearing essential oils. Plants unarmed. Annual. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Young stems tetragonal. To 0.15–0.4 m high. Leaves small; not fasciculate; opposite; decussate; not imbricate; petiolate; foetid; simple; epulvinate. Leaf blades dissected to entire; flat; broad ovate, or orbicular; somewhat palmately lobed; pinnately veined, or pinnately veined to palmately veined; cross-venulate; truncate to cordate. Leaves without stipules. Leaf blade margins crenate; flat. Leaves without a persistent basal meristem. Leaf anatomy. 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 many-flowered. Flowers in verticils. The terminal inflorescence unit cymose. Inflorescences axillary; leafy, thyrse-like with sessile cymes in each axil. Flowers sessile; small; 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; imbricate, or open in bud; campanulate, or funnel-shaped, or tubular; regular; non-fleshy; persistent; with the median member posterior. Calyx lobes narrowly ovate. Corolla present; supposedly 5; 1 -whorled; gamopetalous; blunt-lobed; imbricate; bilabiate (‘lower lobe oblong-spathulate, lateral lobes short and broad, upper lobes narrow-obovate and hooded’); hairy abaxially; with contrasting markings; pale pink (to rose, with darker spots). Corolla lobes oblong (to spathulate), or obovate (obovate). 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; 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. Anthers connivent, or separate from one another; dorsifixed; versatile, or non-versatile; dehiscing via longitudinal slits; introrse; bilocular (loculi strongly divergent); 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’; not becoming exserted. Stigmas 2, or 1 (by reduction); 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, 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 separated by extended internodes. 3–20 flowers subtended by each floral leaf (?—mostly in dense whorls). Calyx limb 5 lobed. Corolla tube exceeding the calyx to not exceeding the calyx. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla entire, or entire to bilobed (sometimes slightly notched); upper (adaxial) lip of the corolla markedly concave. Lower (abaxial) lip of the corolla 3 lobed (the laterals very small, each with a small tooth). Stamens ascending.

Geography, cytology, number of species. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Queensland, New South Wales, and Victoria. A genus of ca 50 species; 1 species in Western Australia; 1 endemic to Western Australia.

Etymology. From the Latin name for the plant.