Aquatic or semi-acquatic herbs (rarely subshrubs), often creeping and rooting at nodes, resinous. Leaves opposite or whorled, simple, entire or toothed; stipules present, scarious. Flowers small, solitary in leaf-axils, or in small axillary cymes, bisexual, actinomorphic; sepals 2–6, free or fused in lower half; petals equal in number to sepals; stamens as many as or twice the number of petals, anthers opening by longitudinal slits; ovary superior, 2–5-locular (but incompletely divided in Bergia); ovules numerous. Fruit a septicidal capsule or schizocarp; seeds lacking endosperm.
2 genera and c. 40 species, widespread in tropics and temperate regions; 2 genera with 6 species in Australia.