Perennial, monoecious, rhizomatous, submerged herbs. Stipules free or sheathing. Flowers axillary. Spathe hyaline, deciduous, cupshaped. 1 male and 2-5 female flowers, often in the same spathe. Perianth absent. Male flower of 1 stamen, filament slender. Female flower of 2-9 carpels; ovary unilocular, ovule 1, pendulous, apical, style short or long, stigma flattened, peltate or ligu¬late. Fruit of 2-9 stalked curved achenes, entire or toothed along one or both margins.