Habit and leaf form. Shrubs; evergreen; bearing essential oils. Plants with neither basal nor terminal concentrations of leaves; to 0.5–3.5 m high. Leptocaul. Helophytic to xerophytic. Leaves minute to small; opposite; decussate; ‘herbaceous’, or leathery; petiolate, or subsessile, or sessile; gland-dotted; aromatic; edgewise to the stem, or with ‘normal’ orientation; simple; peltate, or not peltate; epulvinate. Leaf blades dorsiventral, or isobilateral, or centric; entire; flat; linear, or lanceolate, or oblong, or ovate; linear, or ovate, or obovate, or oblong, or elliptic, or orbicular; pinnately veined, or parallel-veined, or one-veined; cross-venulate, or without cross-venules. Leaves without stipules; without a persistent basal meristem. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous, or ornithophilous. Pollination mechanism conspicuously specialized, or unspecialized.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; axillary. Inflorescences simple, or compound. The terminal inflorescence unit cymose. Inflorescences axillary; of 2–3 flowers, subtended by 2 conduplicate bracts; conflorescences, if present, resembling a terminal or subterminal spike-like raceme. Flowers pedicellate to sessile; (bi) bracteolate. Bracteoles persistent, or deciduous. Flowers minute to small; regular; 5 merous; cyclic. Free hypanthium present (petals ‘inserted on the calyx’); campanulate, or obconic, or turbinate, or urceolate. Hypogynous disk present. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; polysepalous; imbricate; regular; often persistent, or not persistent. Sepals elliptic, or ovate, or triangular, or orbicular. Corolla present; 5; 1 -whorled; polypetalous; imbricate; regular; pink, or white, or yellow (rare). Petals elliptic, or oblong, or obovate, or orbicular; clawed, or sessile. Androecial members definite in number. Androecium 5, or 10 (occasionally a few 5-stamened flowers may be present in an otherwise 10-stamened species). Androecial members unbranched. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; all equal, or markedly unequal (when 10, the antepetalous members slightly longer than the antesepalous); free of one another; 1 -whorled, or 2 -whorled. Stamens 5, or 10; attached on the rim of the hypanthium (borne on a narrow staminophore); becoming exserted (not exceeding the corolla), or remaining included; not didynamous, not tetradynamous; all more or less similar in shape; isomerous with the perianth, or diplostemonous; alternisepalous, or oppositisepalous; erect in bud, or inflexed in bud. Filaments geniculate. Anthers all alike; dorsifixed; versatile, or non-versatile; dehiscing via longitudinal slits, or dehiscing via pores (dehiscing by linear stomia converging above); introrse; unilocular, or bilocular; bisporangiate (rarely apparently unisporangiate); appendaged (the connective with a large gland situated at an apparent right angle bend at the top of the filament, so that the anther is borne towards the style, producing the geniculate or hammer-like stamen characteristic of this genus). Gynoecium 2–5(–16) carpelled. The pistil 1 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; inferior, or partly inferior. Ovary unilocular; 1 locular. Epigynous disk present, or absent. Gynoecium stylate. Styles 1; simple; apical to lateral (central to excentric). Stigmas 1. Placentation parietal to apical (coincident with the position of the style). Ovules in the single cavity 4–8; pendulous to ascending (the ovules arranged radially on the peltate placenta); non-arillate; anatropous.
Fruit and seed features. Fruit non-fleshy; indehiscent; a berry, or a drupe, or a nut; 1 seeded (usually filling the fruit). Seeds non-endospermic; small. Cotyledons 2.
Geography, cytology, number of species. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia. South-West Botanical Province.
B.L. Rye, M.D. Barrett, T.D. Macfarlane, N.S. Lander, M.E. Trudgen, N.G. Marchant, K.R. Thiele