Habit and leaf form. Shrubs, or herbs, or trees (rarely); with coloured juice, or non-laticiferous and without coloured juice; bearing essential oils, or without essential oils; resinous, or not resinous. Young stems of herbs tetragonal. Mesophytic. Leaves opposite; ‘herbaceous’; sessile; gland-dotted; without marked odour; simple; epulvinate. Leaf blades entire; without prominent lateral veins; cross-venulate. Leaves without stipules. Leaf blade margins entire. Leaves without a persistent basal meristem. Stem anatomy. Nodes unilacunar. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, axillary. Inflorescence few-flowered to many-flowered. Flowers in cymes. The terminal inflorescence unit cymose. Inflorescences terminal. Flowers bracteolate, or ebracteolate; small to medium-sized; regular; cyclic, or partially acyclic. Free hypanthium absent. Hypogynous disk absent, or present; of separate members. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous; free; yellow to orange. Calyx 5; 1 -whorled; polysepalous; imbricate; regular; persistent. Corolla 5; 1 -whorled; polypetalous; imbricate, or contorted; regular; yellow to orange. Petals clawed, or sessile. Androecium 20–50 (i.e. ‘many’). Androecial sequence determinable, or not determinable. Androecial members maturing centrifugally; free of the perianth; free of one another. Androecium exclusively of fertile stamens, or including staminodes. Stamens 20–50 (‘many’); polystemonous. Filaments filiform. Anthers globular, with a minute gland at the apex; dehiscing via longitudinal slits; introrse, or extrorse; bisporangiate. Pollen shed in aggregates, or shed as single grains. Gynoecium 1–3 carpelled. The pistil 1–3 celled. Gynoecium syncarpous; synovarious; superior. Ovary unilocular, or plurilocular; 1–3 locular (as many locules as G, or unilocular by intruded placentae failing to reach the middle). Gynoecium stylate. Styles 3 (in H. gramineum); free; attenuate from the ovary; apical. Stigmas 3; wet type; non-papillate; Group IV type. Placentation when ovary unilocular, parietal (on intruded placentae). Ovules 10–50 per locule (i.e., numerous); horizontal, or ascending; arillate, or non-arillate; anatropous, or hemianatropous.
Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules septicidal. Fruit numerous-seeded. Seeds cylindric; non-endospermic; winged, or wingless. Embryo rudimentary at the time of seed release to well differentiated. Cotyledons 2 (sometimes reduced ?). Embryo straight to curved.
Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. Northern Botanical Province, Eremaean Botanical Province, and South-West Botanical Province.