Perennial shrubs or herbs, erect or spreading and rooting at nodes, often aquatic, sometimes submerged parts bearing pneumatophores. Leaves alternate or opposite, rarely whorled, usually entire. Flowers usually solitary or clustered in upper leaf axils, sometimes in an inflorescence; bracteoles often present. Flowers actinomorphic; hypanthium not prolonged beyond ovary; sepals 3–7, persistent; petals usually 4 or 5, or absent; stamens usually as many as or twice as many as sepals; ovary with cells usually equal in number to sepals. Fruit an irregularly dehiscent capsule; seeds free or embedded in the endocarp.
About 82 species, cosmopolitan but best represented in tropical America; 7 species in Australia, 4 native, 2 naturalised and 1 of uncertain status.