Plants perennial, of fresh or brackish waters. Rhizomes present, stolons absent. Erect stems rooted in substrate, branched or unbranched, elongate. Leaves cauline, whorled, 3--8 per node, submersed, sessile; blade linear, rarely slightly elliptic, base tapering to stem, apex acute; midvein without lacunae along side(s), blade uniform in color throughout; abaxial surface ly with prickles along midvein, without aerenchyma; intravaginal squamules fringed with orange-brown hairs. Inflorescences 1-flowered, sessile to subsessile; spathe not winged. Flowers unisexual, staminate and pistillate on different plants or on same plants, submersed, sessile; petals whitish to reddish. Staminate flowers: filaments distinct, released under water, rising to surface; anthers oval; pollen in monads; . pPistillate flowers: ovary 1-locular; floral tube long, styles 1, not 2-fid. Fruits linear, cylindric, smooth or with simple spiny processes, indehiscent. Seeds cylindric, glabrous.