Monoec. or dioec. Infl. of 1 to few minute unisexual fls enclosed within sheathing lf-bases. Per. 0 or represented by 3 membr. scales. Stamen solitary or 2–3; anthers 1–2-celled, dehiscing longitudinally; pollen globular or threadlike. Carpels 1–9, free, sessile or shortly stipitate; style simple or 2–4-lobed, stigmas capitate to funnelform; ovule solitary, pend., strongly curved. Fr. beaked with persistent style-base, indehiscent. Seed without endosperm. Aquatic, rhizomatous, perennial, glab. herbs of fresh, brackish or salt water, us. submerged. Lvs simple, narrowly linear, almost filiform, alt., but sts crowded as though whorled; stipules sheathing or open, either free throughout or adnate to lf-base except for free ligule or auricles. Genera 6, one widespread in temperate waters.