Prostanthera Labill.

Scientific Description

Common name. Mintbushes. Family Lamiaceae.

Habit and leaf form. Shrubs (or undershrubs, rarely trees); evergreen; bearing essential oils. Plants unarmed. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Young stems usually tetragonal. To 0.2–1.5 m high. Leptocaul. Leaves minute to small; not fasciculate; opposite, or whorled (rarely); sub- decurrent on the stems; ‘herbaceous’; not imbricate; petiolate; usually aromatic; simple; epulvinate. Leaf blades entire; flat; narrow ovate, or linear, or elliptic (broad); one-veined, or pinnately veined; cross-venulate; cordate to cuneate at the base, or rounded at the base. Mature leaf blades adaxially glabrous, or scabrous; abaxially glabrous, or scabrous. Leaves without stipules. Leaf blade margins entire; flat, or revolute. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; glandular hairs present; complex hairs absent. Branched 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. Plants heterostylous. 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 panicles, or in verticils, or in racemes. The terminal inflorescence unit cymose. Inflorescences terminal, or axillary; axillary or in terminal botryoid or paniculate inflorescences. Flowers pedicellate; bracteolate. Bracteoles not adnate to the receptacle. Flowers small to medium-sized; 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; disguisedly 5; 1 -whorled; gamosepalous; blunt-lobed; imbricate, or open in bud; exceeded by the corolla (usually), or more or less equalling the corolla; campanulate, or funnel-shaped, or tubular; bilabiate; green, or purple (maroon); non-fleshy; persistent; accrescent (and frequently conspicuously coloured); with the median member posterior. Corolla present; disguisedly 5; 1 -whorled; gamopetalous; blunt-lobed; imbricate; bilabiate (the tube usually expanded in the throat, the lower lip usually spreading (particularly in section Prostanthera), 3-lobed; upper lip erect or extended forward (section Klanderia), emarginate or 2-lobed); with contrasting markings; purple to blue to white (section Prostanthera), or red, or blue to red (metallic; section Klanderia), or pink (bright), or yellow (tinged). Corolla lobes ovate (to broadly). 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 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; 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; bilocular; tetrasporangiate; appendaged (with connective often elongated into an appendage), or unappendaged. The anther appendages basal. 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; attenuate from the ovary, or from a depression at the top of the ovary; apical; 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 (mostly), or indehiscent (perhaps, in Eichlerago). 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 spicate inflorescences, or separated by extended internodes. 1 flowers subtended by each floral leaf. Calyx limb 2–5 lobed. Upper lip of calyx entire, or lobed; when segmented, 3 lobed. Lower lip of calyx entire, or lobed; when segmented, 2 lobed. Corolla tube exceeding the calyx, or exceeding the calyx to not exceeding the calyx; curved. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla entire to bilobed. Lower (abaxial) lip of the corolla 3 lobed (spreading). Stamens ascending. The anterior pair of stamens exceeding the posterior pair.

Geography, cytology, number of species. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. A genus of ca 100 species; 28 species in Western Australia; 14 endemic to Western Australia (taken from CAVP).

Etymology. From the Greek "an addition, appendage" and "anther"; there are small appendages on the anthers.