Habit and leaf form. Shrubs, or herbs; non-laticiferous and without coloured juice. Leaves well developed, or much reduced, or absent (in A. xiphoclada). Plants succulent, or non-succulent. Herbs perennial (with a woody rootstock). Self supporting, or climbing. Mesophytic, or xerophytic. Leaves small to medium-sized; alternate; spiral, or distichous; ‘herbaceous’, or leathery, or fleshy; petiolate to sessile; non-sheathing; gland-dotted, or not gland-dotted; simple. Leaf blades entire; flat, or rolled; pinnately veined, or palmately veined. Leaves with stipules. Stipules entire or lacerate-fringed or fimbriate; caducous, or persistent. Leaf blade margins entire, or dentate; flat, or involute. Leaves without a persistent basal meristem. Leaf anatomy. Urticating hairs present, or absent. Stem anatomy. Nodes tri-lacunar, or unilacunar. Secondary thickening developing from a conventional cambial ring, or anomalous; from a single cambial ring.
Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Unisexual flowers present. Plants dioecious, or monoecious (with male flowers subtending 1(-3) female flowers in each unit of the flower cluster). Female flowers without staminodes. Male flowers aggregated in ‘inflorescences’; without pistillodes. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescences simple, or compound; terminal (on branchlets), or axillary; of small sessile clusters surrounded by scarious bracts. Flowers pedicellate to sessile; bracteate; small; regular; 3–6 merous. Free hypanthium absent. Hypogynous disk present, or absent. Perianth sepaline; 3–6; 1 -whorled. Calyx present; 3–5(–6) (in male flowers), or (4–)5 (in female flowers); 1 -whorled; gamosepalous (connate in the lower half in male flowers; connate only towards the base in female flowers); valvate; regular; persistent; non-accrescent. Calyx lobes entire in male flowers, fringed on upper margin of female flowers. Corolla absent. Fertile stamens present, or absent (female flowers). Androecium 2–10 (occasionally surrounded by as many small glands as perianth lobes). Androecial members free of the perianth; all equal, or markedly unequal (when stamens more numerous than perianth lobes); free of one another, or coherent (filaments shortly united at the base); 1 -whorled, or 2 -whorled. Androecium exclusively of fertile stamens. Stamens 2–10; becoming exserted; reduced in number relative to the adjacent perianth, or isomerous with the perianth, or diplostemonous; erect in bud, or inflexed in bud. Anthers pendant from the often glandular top of filaments; dehiscing via longitudinal slits; extrorse, or introrse; usually bilocular; bisporangiate, or tetrasporangiate; usually the connective tipped with a small gland. Fertile gynoecium present, or absent (male flowers). Gynoecium 3 carpelled. The pistil 3 celled. Gynoecium syncarpous; synovarious, or synstylovarious (depending on interpretation of partially connate styles); superior. Ovary plurilocular; 3 locular. Styles 3(–4); free, or partially joined (shortly connate at the base); forked (each forming 2 stigmatic branches); apical. Stigmas 6(–8); dry type; papillate, or non-papillate; Group II type. Placentation axile, or apical. Ovules 1 per locule; pendulous; epitropous; with ventral raphe, or with dorsal raphe; arillate; anatropous.
Fruit and seed features. Fruit non-fleshy; a schizocarp (an ovoid capsule). Mericarps 3; 2-valved. Fruit elastically dehiscent (schizocarpic capsules often splitting elastically), or passively dehiscent; 0–3 seeded. Seeds 1 per mericarp. Seeds ovoid to oblong; endospermic. Endosperm oily. Seeds arillate. Cotyledons 2. Embryo linear, straight, or curved. Testa smooth. Seedling. Germination phanerocotylar, or cryptocotylar.
Physiology, biochemistry. Mustard-oils present, or absent.
Geography, cytology, number of species. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia, South Australia, Queensland, New South Wales, Victoria, and Tasmania. South-West Botanical Province.
Additional characters Fruit with 6 erect appendages at the apex.