Mentha L.

Scientific Description

Common name. Mints. Family Lamiaceae.

Habit and leaf form. Herbs; evergreen; bearing essential oils. Plants unarmed. Perennial. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Young stems tetragonal. To 0.08–0.9 m high; rhizomatous. Leaves small to medium-sized; not fasciculate; opposite; not decurrent on the stems; not imbricate; sessile, or subsessile, or petiolate; aromatic; simple; epulvinate. Leaf blades entire; flat; ovate (to narrowly), or elliptic (to narrowly), or orbicular (almost); pinnately veined; cross-venulate; cordate to cuneate at the base, or rounded at the base. Mature leaf blades adaxially glabrous, or scabrous (sparsely), or pilose (to densely); abaxially glabrous, or scabrous, or pilose, or woolly (grey or white). Leaves without stipules. Leaf blade margins crenate to serrate; flat. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; glandular hairs present; complex hairs present. Branched hairs present and absent. Urticating hairs absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite, or hermaphrodite and functionally female. Unisexual flowers present, or absent. Plants hermaphrodite, or gynomonoecious. Plants heterostylous. 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 terminal; a terminal head or spike of many flowered verticillasters. Flowers sessile, or pedicellate; bracteate; small; 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; prominently 10–15 veined; imbricate, or open in bud; campanulate, or tubular; regular to unequal but not bilabiate; non-fleshy; persistent; with the median member posterior. Calyx lobes narrowly triangular, or triangular. Corolla present; ostensibly 4, or 5 (the adaxial segment being often notched or emarginate); 1 -whorled; gamopetalous; blunt-lobed; imbricate; regular, or regular to unequal but not bilabiate (at the most only very weakly two lipped — with 4 almost equal lobes, the upper one broadest and emarginate or 2-lobed); hairy abaxially, or glabrous abaxially; plain; violet, or pink, or white. Corolla lobes oblong, or ovate. 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 in the throat of the corolla tube. Stamens becoming exserted, or remaining included; not didynamous, not tetradynamous; 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 glabrous; filiform. Anthers separate from one another; dorsifixed; versatile, or non-versatile; dehiscing via longitudinal slits; introrse; unilocular to bilocular; 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’; 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, 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, or separated by extended internodes. 5–25 flowers subtended by each floral leaf (‘many’). Calyx limb 5 lobed.

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. 30 species; 4 species in Western Australia; 0 endemic to Western Australia.

Etymology. From the Latin for "mint"; from the name of a nymph, Minthe, who was turned into mint by Proserpine, the jealous wife of the god Pluto.