Prostrate or diffuse, annual or perennial herbs, sometimes becoming woody at the base. Leaves opposite, entire, linear, terete or flat, glabrous or papillose; petiole dilated at base. Flowers axillary, clustered, sessile, each subtended by one or more bracts; perianth segments 5, fused into a short tube, lobes unequal, margins scarious, sometimes with a small dorsal mucro below the apex; stamens 5–many, fused to perianth tube; ovary superior to half-inferior, 1-locular; style 1; ovules 2–many. Fruit a membranous or woody circumsciss capsule, the ‘lid’ usually splitting near the base, perianth usually persistent; seeds 1–many, triangular, reniform or comma-shaped, smooth or patterned, often pappilose, black.
About 30 species throughout the tropics and subtropics; 15 or 16 species in Australia (most are endemic).