Herbs or undershrubs, often aquatic, monoecious, polygamous or dioecious. Stipules 0 (but see note under Myriophyllum). Leaves alternate, opposite or whorled, simple or pinnatifid. Calyx lobes and petals 2-4 or 0, free. Stamens (0-1-)2-4 or 8. Ovary inferior, 1-4-locular. Fruit a nutlet, indehiscent or breaking up into 2 or 4 one-seeded mericarps, or a drupe.
Worldwide: 10 genera and 185 species, cosmopolitan but especially southern hemisphere.