Erect or floating aquatic perennials. Leaves aerial, or with floating and/or emersed laminae sheathing at base. Flowers bisexual, actinomorphic or ± zygomorphic, solitary, or in spikes, racemes or panicles with a sheathing bract. Perianth petaloid, hypogynous; lobes 6, ± 2-seriate, free or connate below in a tube. Stamens 1, 3, or 6, equal or unequal, inserted at different levels on throat; filaments free; anthers 2-celled, dehiscing by longitudinal slits or rarely by terminal pores. Ovary superior, 1- or 3-locular; style filiform; stigma entire or shortly 3-lobed or 6-toothed; ovules 1 or many. Fruit indehiscent or a loculicidal capsule. Seeds longitudinally ribbed. Genera 7, in fresh water in tropical and subtropical regions.