Sp. Pl. 2: 970. 1753.
Roots to 15 cm, tip mostly rounded; sheath not winged. Stipes white, thin, often decaying. Fronds floating, 1 or 2–5 or more, coherent in groups, obovate, often gibbous, 1–8 mm, 1–1.5 times as long as wide, margins entire; veins (3–)4–5(–7) (all originating from node), greatest distance between lateral veins near or distal to middle; papillae often indistinct; upper lower surface sometimes red colored, coloring beginning from margin, lower upper surface occasionally with distinct red spots beginning from margins near apex; largest air spaces longer than 0.3 mm; distinct turions absent. Flowers: ovaries (1–)2–7-ovulate, utricular scale with narrow opening at apex. Fruits 0.6–1 mm, laterally winged. Seeds with 8–16 distinct ribs, falling out of fruit wall after ripening. 2n = 40, 42, 44, 50.
Phenology: Flowering (rather frequent) spring–fall.
Habitat: Eutrophic, quiet waters in temperate regions with mild winters
Elevation: 0–1900 m
Ariz., Calif., Ill., Nebr., Nev., N.Mex., Tex., Wyo., northern Mexico, South America, Eurasia, Africa, Atlantic Islands.