Slender-stemmed perennial herbs, less commonly erect shrubs. Underwater parts often swollen, spongy or bearing inflated pneumatophores. Lvs alternate or opposite, simple, mostly entire. Fls axillary, actinomorphic, solitary or clustered in spikes or heads. Floral tube not prolonged beyond ovary. Sepals 3-7, ± persistent at fruiting. Petals as many as sepals or 0, yellow or white. Stamens as many or twice as many as sepals; anthers usually versatile. Stigma entire or 4-lobed; ovary cells 4. Capsule variously shaped, dehiscent by terminal pores or longitudinal flaps. Seeds numerous, small, free or embedded in the woody endocarp.