Annual or perennial, prostrate to ascending, succulent herbs. Leaves alternate or subopposite, often upper ones crowded in a foliar involucre around flowers, flat or terete, sometimes succulent; stipules scarious, fimbriate or present as tufts of hairs, rarely absent. Inflorescences of subapical flowers, clustered in a capituliform cyme or solitary. Sepals 2, opposite, free or connate below, unequal, usually persistent; petals (4-)5(-6), free or connate at base, falling off rapidly; stamens 4-8 or more, basipetalous, filaments often pubescent below; ovary inferior of half-inferior, ovules numerous, styles 2-9, united below, rarely free. Fruit a 1-locular, membranous or chartaceous, circumscissile capsule; seeds numerous, reniform or cochleate, testa smooth or tuberculate.