Annales des Sciences Naturelles, Botanique sér. 3, 11: 79. 1849.
Plants perennial, of fresh waters. Rhizomes and stolons absent. Erect stems rooted in substrate, branched or unbranched, elongate. Leaves cauline, in whorls of 5 or more [opposite], submersed, sessile; blade linear, base sloping to stem, apex obtuse; midvein without rows of lacunae along side(s), blade uniform in color throughout;; abaxially surface without prickles or aerenchyma; intravaginal squamules entire. Inflorescences 1-flowered, sessile; spathes not winged. Flowers unisexual, staminate and pistillate on different plants, projected to surface by slender, elongate floral tube base, pedicellate; petals white. Staminate flowers: filaments distinct; anthers linear; pollen in monads. Pistillate flowers: ovary 1-locular; styles 3, not 2-fid. Fruits ovoid, smooth, dehiscing irregularly. Seeds fusiform, mucilaginous.
Introduced; North America, Central America, South America, Eurasia, Africa, Australia.
Species 2 (1 in the flora).