Annual, glabrous, prostrate, much branching, 10-50 cm. Branches fleshy, brittle, very leafy. Leaves 1-2 cm., opposite, sessile, fleshy, obovate-oblong, entire, dark green. Flowers sessile in dense forks. Sepals unequal, up to 2 mm. broad, obtuse, keeled beneath apex. Petals about as long as sepals, ovate-oblong, retuse, open in the morning only. Stamens 8-15. Capsule 0.6-1 cm., many-seeded, pyriform-rhomboidal, opening by a lid. Seeds 0.5-1 mm. across, black, tuberculate or granulate, or smooth. 2n = 36, 54. Fl. mainly February-September.