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.
Much like Elodea, but the fls more showy, nectariferous, and insect- pollinated; pet much longer than the sep; dioecious; fls of both sexes elevated to the surface by the slender, pedicel-like hypanthium; staminate spathes 2-4-fld; staminate fls with 9 distinct stamens and a small central nectary; filaments elongate; anthers short, each pollen-sac opening longitudinally, not explosive; pistillate spathes split half way down one side; style deeply trifid, each segment deeply 2-3-cleft and with a small nectary externally at the base of each lobe; lower lvs opposite or ternate, the others in whorls of 4-8. 2, S. Amer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.