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Perennial, submerged fresh-water herbs, with an erect main axis,-rooting basally, the roots unbranched, smooth, the stem slender, unbranched or slightly to moderately branched. Leaves not differentiated into blade and petiole, linear or lanceolate, rarely elliptic, translucent, green, with many tannin cells, acute apically, the margin serrate, with 1 medium nerve, at most 4 cm long, the lower alternate or in whorls of 3, usually reduced in size, the middle and upper in whorls of 3-8; squamulae intravaginales 2, minute, fringed. Inflorescences axillary, sessile or subsessile, 1-flowered; spathe of 2 connate bracts. Flowers unisexual, the plants dioecious; staminate spathe subsessile, globose, dorso-ventrally flat-tened, with subulate appendages and a minute central knob; staminate flower freely-floating, pedicellate, the sepals 3, ovate to oblong-elliptic, strongly convex, reflexed, the petals 3, linear to spatulate, narrower than the sepals, spreading to reflexed, the stamens 3, the anthers erect, 4-thecate, latrorsely dehiscent; carpellate spathe sessile, tubular, bifid, membranous; carpellate flower sessile, with a long hypanthium, the sepals 3, oblong to obovate, convex, the petals 3, spatulate, narrower than the sepals, the ovary linear, unilocular with 3 parietal placentas, the ovules several, ortho-to anatropous, the styles 3, filiform to subulate, entire. Fruits linear, cylindrical; seeds cylindrical, glabrous, 2-6 in a row.
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.
Monoecious or dioecious, caulescent. Leaves in whorls of 3-8, sessile, linear to lanceolate, rarely elliptic; midrib conspicuous. Flowers unisexual. Male spathe subsessile, solitary in the leaf axils, flattened globose, liberating a solitary, small, pedicelled ♂ flower. Sepals 3, strongly convex, imbricate; petals 3, imbricate. Stamens 3, alternating with the petals; anthers erect, latrorsely dehiscent. Female spathe sessile, solitary in the leaf axils, cylindrical, top bifid, membraneous, containing a solitary ♀ flower. Sepals 3, imbricate, convex; petals 3, imbricate. Ovary cylindric to narrowly conical; beak filiform; styles 3, alternipetalous. Fruit cylindrical or narrowly conical. Seeds 2-6, oblong-elliptic.
Herbs, submerged. Stems elongated, branched. Leaves verticillate or lowermost opposite, sessile, linear to narrowly elliptic, margin serrate with 2 small, fringed nodal scales. Plants dioecious or monoecious; flowers unisexual, axillary. Male spathe subsessile, membranous, subglobose, with apical knob and corona of setae, 1-flowered; male flowers shortly pedicellate, free from spathe on water surface at anthesis; sepals 3, ovate or obovate, convex; petals 3, narrower than sepals; stamens 3. Female spathe tubular, sessile, bifid at apex, 1-flowered; sepals and petals similar to male ones; ovary cylindric, attenuate into a filiform beak; styles (2 or)3; ovules few. Fruit cylindric or linear.
Freshwater, monoecious or dioecious, perennial, attached aquatic, with unbranched roots; internodes evenly spaced. Leaves submerged, cauline, mostly >3-whorled, not differentiated into blade and sheath, with midrib. Inflorescences floating, usually 1-flowered, unisexual, axillary. Flowers with 2 perianth whorls each of 3 segments, ±equal in size. Male flowers separating when in bud and rising to water surface, opening when free-floating, both perianth whorls then reflexed; spathe sessile in leaf axils; hypanthium absent; stamens 3. Female flowers with thread-like hypanthium; staminodes 3, minute; carpels 3; styles 3. Fruit ±cylindric. Seeds 2–6.
Much like Elodea; monoecious or dioecious; stamens 3, principal lvs in whorls of 3–8; stipules fringed. 1, originally Old World.
