Small annual or perennial herbs. Leaves opposite, small or pseudo-verticillate. Stipules scarious. Inflorescence in dense or loose cymes. Flowers small. Sepals 5, free, green, carinate with scarious margin. Petals 5 or fewer, shorter than sepals. Stamens 5 or fewer, opposite to the sepals; Ovary unilocular; Capsule shorter than sepals, splitting almost to base into 3 spirally twisting valves. Seeds ovoid to lenticular.
South America present, the Mediterranean present, tropical Asia present
About 18 closely related species distributed throughout the Mediterranean region, 2 species in South America, 2 species in tropical Asia.