A family of submerged, perennial, aquatic, monocotyledonous (see monocotyledon) herbs of fresh or salt water, comprising plants that have slender, creeping rhizomes, and stems bearing narrow, linear, opposite, whorled, or alternate leaves, with sheathing bases, and tiny flowers, solitary in leaf axils or in small clusters. The flowers are unisexual. There is either no perianth, or one composed of 3 tiny scales. Male flowers have 1–3 stamens, with 1 or 2 anther cells, while in female flowers up to 9 carpels are free from each other and terminate in a long beak bearing the stigma. Pollination occurs under water, and the fruits are achenes. There are 4 genera, with some 7 cosmopolitan species.
Subjects: Plant Sciences and Forestry.