Succulent annual or perennial herbs, stems prostrate, ascending or twining. Leaves alternate or opposite, mostly basal, sometimes appearing rosetted, becoming progressively smaller toward branch-tips, usually sessile, terete to flat or concave on upper surface; axillary hairs absent. Flowers few–many, in contracted or elongating cymes; bracts alternate to opposite; sepals free, usually persistent in fruit; petals 4–11 (commonly 5), free, white to purplish; stamens 3–many; ovary superior, ovules 1–many, style cleft into 3 or 4 stigmatic arms. Capsule longitudinally dehiscent or opening via a terminal pore; seeds ovate to reniform, smooth or the testa variably patterned.
About 120 species from Australia and the Americas; c. 40 species in Australia.