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Plants perennial, of fresh or brackish waters. Rhizomes and stolons present. Erect stems rooted in substrate, unbranched, short. Leaves basal, submersed, sessile; blade linear, base grading into sheath, apex obtuse to apiculate; midvein with 4--5 rows of lacunae on each side, balde appearing 3-zoned with light-colored middle zone bordered on each side by darker zone; abaxial surfacely without prickles or aerenchyma; intravaginal squamules entire. Inflorescences cymose, long-pedunculate; spathe not winged. Flowers unisexual, staminate and pistillate on different plants, submersed or floating, sessile (staminate) or pedicellate (pistillate); petals transparent. Staminate flowers: filaments distinct, released from spathe and floating to surface; anthers spheric; pollen in monads. Pistillate flowers floating; ovary 1-locular; styles 1, not 2-fid. Fruits cylindric to ellipsoid, ridged, dehiscing irregularly. Seeds ellipsoid, glabrous.
Herbs, submerged, stoloniferous, without erect stems. Leaves basal, sessile, linear or strap-shaped, veins 3-9, parallel, slightly sheathed at base, margin minutely serrulate or entire. Plants dioecious; flowers unisexual. Male flowers numerous, minute, shortly pedicellate, clustered together on a central column enclosed by a common spathe, each flower finally breaking free and floating on water surface; spathe ovate or broadly lanceolate, shortly pedunculate; sepals 3, convex, 2 larger than other; petals 2 or 3, minute; stamens 1-3. Female flowers solitary in spathe; spathe tubular, bifid at apex, pedunculate; peduncles long, coiled after anthesis; sepals 3; petals 3, minute; ovary narrowly cylindric or narrowly triangular-cylindric; ovules numerous; styles 3, bifid. Fruit cylindric or triangular-cylindric. Seeds numerous, oblong or fusiform.
Glabrous, dioecious. Leaves radical, linear, sheathing at the base, with longitudinal air-channels; apex obtuse, margin faintly dentate or entire; nerves 3-9, parallel, connected by cross-veins, only the midrib reaching the apex, the other nerves gradually joining together near the top. Male spathe only shortly peduncled, smaller than the female one, containing many pedicelled flowers which break off and rise to the surface. Sepals 3, ovate or oblong-ovate, convex. Petals 3, minute. Stamens 1-3. Female spathe connate, tubular with 2 rounded tops; peduncle very long, spirally contracted after anthesis. Sepals 3, ovate or oblong-ovate. Petals 3, minute, scarious. Ovary linear, nodding; styles 3, split into 2 lobes. Fruit linear, often very long. Seeds ∞ oblong to fusiform; testa membranous.
Dioecious; staminate fls minute, numerous in a head subtended by a short-pedunculate, ovoid, bivalved spathe arising from the base, with 3 sep (one smaller), one pet-vestige, and 2 stamens, the fls at anthesis separating individually and floating to the surface; pistillate fls mostly solitary and sessile in a tubular, apically bifid spathe on a long, slender scape (reaching the surface), with 3 sep, 3 pet-vestiges, 3 staminodia, and 3 broad, bifid stigmas; pistillate scape coiling after anthesis and retracting the fr; ovules scattered over the ovary-wall; fr elongate, cylindric, indehiscent, many-seeded; vigorously stoloniferous, aquatic perennials with long, ribbon-like basal submersed lvs from a very short, erect crown. 2, cosmop.
