Habit and leaf form. Trees, or shrubs; evergreen; bearing essential oils. Plants unarmed. Leaves cauline. Young stems cylindrical, or tetragonal (obtusely). To 0.5–10 m high. Leptocaul. Leaves small to medium-sized; not fasciculate; opposite; decussate; not imbricate; petiolate to sessile; aromatic, or without marked odour, or foetid; simple; epulvinate. Leaf blades entire; flat; broadly ovate, or obovate, or orbicular; pinnately veined; cross-venulate. Mature leaf blades adaxially glabrous, or pubescent (puberulous); abaxially glabrous, or pubescent. Leaves without stipules. Leaf blade margins entire, or crenate, or serrate, or dentate; flat. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present, or absent; 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. Plants heterostylous. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence many-flowered. Flowers in cymes. The terminal inflorescence unit cymose. Inflorescences terminal; a terminal arrangement of pedunculate cymes, often many-branched. Flowers pedicellate, or subsessile; bracteate; minute to small; very irregular; zygomorphic; 4 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present, or absent. Perianth with distinct calyx and corolla; 8–10; 2 -whorled; isomerous, or anisomerous. Calyx present; 4 (ostensibly), or 5; 1 -whorled; gamosepalous; entire to lobed; blunt-lobed, or toothed. Calyx lobes markedly shorter than the tube. Calyx spreading; open in bud; somewhat campanulate, or tubular; more or less bilabiate; persistent; accrescent, or non-accrescent; when K5, with the median member posterior. Calyx lobes more or less ovate. Corolla present; 4 (ostensibly), or 5; 1 -whorled; gamopetalous; lobed; blunt-lobed. Corolla lobes markedly shorter than the tube to about the same length as the tube. Corolla imbricate; campanulate, or tubular; bilabiate; glabrous abaxially, or hairy abaxially (somewhat puberulous); hairy adaxially; with contrasting markings; white, or green to white, or red (reddish or dull brick-red), or green to cream; deciduous. Corolla lobes broadly elliptic, or oblong, or rhombic, or ovate, 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 exclusively of fertile stamens. Stamens 4. Staminal insertion midway down the corolla tube. Stamens becoming exserted, or remaining included; didynamous; all more or less similar in shape; reduced in number relative to the adjacent perianth; oppositisepalous. Filaments glabrous. Anthers connivent, or separate from one another; dorsifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate. Gynoecium 2 carpelled. The pistil 4 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 4 locular. Locules secondarily divided by ‘false septa’. Gynoecium median. Ovary sessile. Ovary summit glabrous. Gynoecium stylate. Styles 1; simple; attenuate from the ovary; apical; much longer than the ovary at anthesis; becoming exserted, or not becoming exserted; hairless. Stigmas 1; 2 - lobed. Placentation axile. Ovules 1 per locule; pendulous, or horizontal, or ascending; non-arillate; hemianatropous.
Fruit and seed features. Fruit 3–8 mm long; fleshy; indehiscent; a drupe. The drupes with one stone. Fruit 4 locular. Dispersal unit the fruit. Seeds non-endospermic. Cotyledons 2 (expanded, flat). Embryo straight.
Special features. Calyx limb 4 lobed, or 5 lobed. Upper lip of calyx entire, or lobed; obscurely 3 lobed. Lower lip of calyx entire, or lobed; 2 lobed. Corolla tube exceeding the calyx; straight. The upper lip of the corolla incorporating 2 members, the lower 3; (posterior, adaxial) lip of the corolla entire to bilobed; upper (adaxial) lip of the corolla not concave. Lower (abaxial) lip of the corolla 3 lobed; not concave.
Geography, cytology, number of species. Native of Australia. Endemic to Australia, or not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, Queensland, and New South Wales. Northern Botanical Province. A genus of ca 200 species; 3 species in Western Australia; 0 endemic to Western Australia.
Etymology. Said to be from the Greek premnon (the bole or stump of a tree), because the original species was a dwarf.