Habit and leaf form. Shrubs; evergreen; bearing essential oils. Plants with neither basal nor terminal concentrations of leaves; to 1.75 m high. Leptocaul. Mesophytic to xerophytic. Leaves minute to small; opposite; decussate; ‘herbaceous’, or leathery; sessile; gland-dotted; aromatic; edgewise to the stem, or with ‘normal’ orientation; simple; epulvinate. Leaf blades dorsiventral, or isobilateral, or centric; entire; flat; linear, or lanceolate, or oblong, or ovate; elliptic; pinnately veined, or parallel-veined, or one-veined; cross-venulate, or without cross-venules. Leaves without stipules. Leaf blade margins entire. Leaves 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 aggregated in ‘inflorescences’; in racemes. Inflorescences simple, or compound. The terminal inflorescence unit cymose. Inflorescences terminal (or subterminal); spike-like, flowers closely appressed. Flowers sessile; (bi) bracteolate. Bracteoles persistent. Flowers minute to small; very irregular; zygomorphic. The floral asymmetry involving the perianth. Flowers 5 merous; cyclic. Free hypanthium present (petals ‘inserted on the calyx’); dorsiventrally compressed, the free part inclined towards the axis. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; polysepalous; imbricate, or valvate; unequal but not bilabiate (the 2 anterior segments larger and the posterior smaller than the other 2). Corolla present; 5; 1 -whorled; polypetalous; imbricate; regular; yellow. Petals elliptic; clawed; hooded (slightly). Androecial members definite in number. Androecium 10. Androecial members unbranched. Androecial sequence determinable, or not determinable. Androecial members free of the perianth; markedly unequal; free of one another; indistinctly 2 -whorled. Stamens 10; attached on the rim of the hypanthium; remaining included; not didynamous, not tetradynamous; distinctly dissimilar in shape; diplostemonous; erect in bud, or inflexed in bud. Filaments appendiculate (the outer, antepetalous stamens with the filament produced into a filiform stipe bearing a large, irregularly shaped or more or less globular appendage above the anther; the inner, antesepalous stamens with a shorter filament and a smaller, ellipsoidal appendage level with the outer anthers); not geniculate. Anthers all alike; dorsifixed; versatile; dehiscing via pores (pore central); introrse; unilocular; trisporangiate, with one microsporangium above and 2 below. Gynoecium 2 carpelled. The pistil 1 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; inferior. Ovary unilocular; 1 locular. Epigynous disk present. Gynoecium stylate. Styles 1; apical; not becoming exserted. Stigmas 1. Placentation lateral within the ovary. Ovules in the single cavity 2; ascending; collateral (above the middle); non-arillate; anatropous.
Fruit and seed features. Fruit non-fleshy; indehiscent; 1 seeded. Seeds non-endospermic; winged, or wingless. 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