Fresh water and marshy perennial herbs; free floating or rooting. Roots adventitious. Leaves submerged or floating. Petioles sheathing at the base. Flowers bisexual, in racemes or spikes, subtended by a spathe-like leaf sheath. Perianth segments 6, free or united. Stamens (1-3-)6, epipetalous, filaments often unequal. Anthers equal or unequal. Ovary 1-3-locular, superior; ovules 1-numerous; placentation parietal, axile or pendulous. Style 1, stigma entire or lobed. Fruit a 3-valved capsule or a nut. Seeds ribbed.