Subfamily Paronychioideae, Tribe Polycarpeae.
Habit and leaf form. Herbs, or shrubs; non-laticiferous and without coloured juice. ‘Normal’ plants. Leaves well developed. Plants with roots. Annual, or perennial. Leaves cauline. Self supporting. Mesophytic. Not heterophyllous. Leaves small; opposite, or whorled (apparently); with blades; sessile; simple; not peltate. Leaf blades entire; linear to ovate. Mature leaf blades adaxially glabrous; abaxially glabrous. Leaves conspicuously with stipules. Stipules scaly (‘scarious’). Leaf blade margins entire. Leaf anatomy. Hairs absent; glandular hairs absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in lax or dense in cymes. Inflorescences compound. The terminal inflorescence unit cymose. Inflorescences terminal. Flowers pedicellate; conspicuously bracteate; small; regular; tetracyclic. Free hypanthium absent. Perianth with distinct calyx and corolla; 10(–13); 2 -whorled; isomerous, or anisomerous (rarely). Calyx present; 5(–8); 1 -whorled; polysepalous; glabrous; imbricate, or valvate (rarely); white, or purple to brown. Corolla present; 5; 1 -whorled; polypetalous; contorted, or imbricate (rarely). Petals oblong to obovate; sessile. Corolla members entire. Androecium present. Fertile stamens present. Androecium (2–)5, or 10 (rarely). Androecial members markedly unequal (when stamens 10, inner members staminodal), or all equal; free of one another; 1 -whorled, or 2 -whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes 0, or 5. Stamens (2–)5; reduced in number relative to the adjacent perianth, or isomerous with the perianth, or diplostemonous (obdiplostemonous). Anthers separate from one another; dehiscing via longitudinal slits; introrse; bilocular; tetrasporangiate. Fertile gynoecium present. Gynoecium 3 carpelled. The pistil 1 celled. Gynoecium syncarpous; synovarious to eu-syncarpous; superior. Ovary unilocular; 1 locular. Gynoecium stylate. Styles 3; partially joined; simple. Stigmas 1 - lobed, or 3 - lobed; capitate. Placentation free central, or basal. Ovules campylotropous.
Fruit and seed features. Fruit ca 0.5 mm long; dehiscent; a capsule. Capsules valvular. Dispersal unit the seed. Fruit 15–40 seeded. Perisperm present. Seeds small, or minute.
Geography, cytology, number of species. Holarctic. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, and New South Wales. 2n=18, ca 26, 36, ca 52. A genus of ca 50 species; 10 species in Western Australia; 0 endemic to Western Australia.
Additional comments. P. spirostylis is a copper indicator in Australia (Bittrich 1993:221).