Habit and leaf form. Low shrubs, or herbs; evergreen; bearing essential oils. Plants unarmed. Perennial. Leaves cauline. Young stems (sub-) cylindrical, or tetragonal (weakly). To 0.5–2.5 m high. Leptocaul. Leaves medium-sized; not fasciculate; opposite; decussate; not imbricate; petiolate; aromatic, or without marked odour, or foetid; simple; epulvinate. Leaf blades entire; flat; ovate, or obovate, or oblong, or elliptic; pinnately veined; cross-venulate; long attenuate at the base (or decurrent into petiole). Mature leaf blades adaxially glabrous; abaxially glabrous, or scabrous (sparsely strigose on veins and margins). Leaves without stipules. Leaf blade margins crenate to serrate, or dentate; flat. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; complex hairs absent. Branched hairs absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence many-flowered. Flowers in spikes. The terminal inflorescence unit racemose. Inflorescences terminal; terminal, elongate, pedunculate spikes, the flowers usually in depressions in a stout axis. Flowers sessile; bracteate; small; somewhat irregular; zygomorphic. The floral asymmetry mainly involving the androecium. Flowers cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present, or absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed; toothed; prominently 5 veined; erect; open in bud; exceeded by the corolla; hypocrateriform, or tubular (below); regular, or unequal but not bilabiate; persistent; non-accrescent; with the median member posterior. Calyx lobes broadly triangular. Corolla present; 5; 1 -whorled; gamopetalous; lobed; blunt-lobed; imbricate; funnel-shaped; somewhat bilabiate; glabrous abaxially; hairy adaxially; plain; pale blue, or violet (pale or lavender), or purple, or white (occasionally). Corolla lobes ovate, or obovate, or trullate, or obtrullate, or triangular, or obtriangular, or linear, or orbicular. Corolla members entire. Androecium present. Androecial members definite in number. Androecium 4. Androecial sequence not determinable. Androecial members adnate (to the corolla tube); markedly unequal; free of one another; 1 -whorled. Androecium including staminodes. Staminodes 2; representing the posterior-lateral pair; non-petaloid. Stamens 2; 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 anterior-lateral pair; oppositisepalous. Filaments hairy; filiform. Anthers connivent, or separate from one another; dorsifixed; dehiscing via longitudinal slits; introrse; bilocular (locules divergent); tetrasporangiate. Gynoecium 1 carpelled (by abortion of the posterior carpel?), or 2 carpelled. The pistil 2 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 1 locular, or 2 locular. Locules secondarily divided by ‘false septa’. Gynoecium median. Ovary summit glabrous. Gynoecium stylate. Styles 1; simple; attenuate from the ovary; apical; much longer than the ovary at anthesis; not becoming exserted; hairless. Stigmas 1; 1 - lobed, or 2 - lobed; capitate. Placentation basal to axile. Ovules 1 per locule (per cell), or 2 per locule; ascending; non-arillate; anatropous.
Fruit and seed features. Fruit 3–4 mm long; non-fleshy; a schizocarp. Mericarps 2; comprising nutlets. Seeds 1 per mericarp. Seeds non-endospermic. Cotyledons 2 (expanded, flat). Embryo straight.
Special features. Calyx limb 5 lobed. Corolla tube exceeding the calyx; curved. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla bilobed; upper (adaxial) lip of the corolla not concave. Lower (abaxial) lip of the corolla 3 lobed; not concave.
Geography, cytology, number of species. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, Queensland, and New South Wales. Northern Botanical Province. A genus of ca 65 species; 1 species in Western Australia; 0 endemic to Western Australia.