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Dioecious, rhizomatous, coarse, marine, submerged plant. Leaves few, 2-6, ribbonlike, together enclosed by a flattened, membranous, transparent sheath, apex inaequilateral, faintly serrulate when juvenile; nerves many, parallel, air-channels numerous, septated. ♂ Inflorescence: a peduncled spathe consisting of 2 connate blades, the margins of the outer one embracing the inner blade. Flowers small, numerous, pedicelled, on a central stipe, caducous just before anthesis and the mature buds rising to the level of the water. Sepals 3. Petals 3. Stamens 3, alternipetalous; anthers subsessile, 2-locular, latrorsely dehiscing; pollen grains very large. ♀ Inflorescence 1-flowered, long-peduncled. Spathe consisting of 2 nearly free blades, one embracing the other with both margins, persistent. Sepals 3. Petals 3. Ovary rostrate, composed of 6 carpels, 1-locular, the 6 parietal placentas far protruding and forming 6 cavities; styles 6, each forked from the base. Ovules ∞, each with 2 integuments, embedded in mucilage. Fruit ovate, acuminate. Seeds 8-14, obconical, angular, containing starch, embryo containing a large suspensor-cell; the integuments simply stretch so much that they equal the growing embryo; when the fruit is ripe and bursts the testa breaks off around the hypocotyle and remains as a ragged, easily loosened cap on top of the cotyledon.
Marine, submerged or intertidal, dioecious, robust, perennial herbs. Rhizomes creeping, monopodially-branched, coarse; internodes short, covered with persistent stiff fibrous remains of old leaves. Roots unbranched, coarse, cork-like. Leaves tufted, 2–6, distichously arranged, differentiated into sheath and blade; ligules absent; blade strap-shaped, entire, rounded or obtuse, glabrous, with many parallel longitudinal veins; tannin cells numerous; stomata absent. Inflorescences axillary, pedunculate with 2 spathe bracts. Male inflorescence with numerous flowers. Male flowers pedicellate, detaching when buds mature and becoming free-floating on water surface; sepals 3; petals 3; stamens 3, alternate to petals; anthers subsessile, bilocular, dehiscing longitudinally; pollen grains large, trinucleate. Female inflorescence 1-flowered, long-pedunculate, reaching to water surface at anthesis; peduncle becoming coiled and contracted after anthesis. Female flowers: sepals 3; petals 3; ovary rostrate; carpels 6, unilocular, with several ovules; styles 6, each forked from base. Fruit ovoid-acuminate, covered by stiff branched appendages, irregularly dehiscent. Seeds 8–14, obconic, angular; testa membranous.
Herbs, submerged marine; rhizome robust, with persistent fibrous remains of leaf sheaths. Leaves 2-6, narrowly linear or ribbon-shaped, sheathing at base, with many parallel veins, unequal at apex. Plants dioecious; flowers unisexual. Male inflorescence shortly pedunculate, enclosed by 2 spathal bracts; flowers numerous, minute, shortly pedicellate, breaking off just before anthesis, floating on surface of water at maturity; tepals reflexed; stamens 3; anthers subsessile, latrorsely dehiscent; pollen grains very large. Female inflorescence 1-flowered, with a long peduncle, enclosed by 2 overlapping, scarcely fused, strongly keeled spathal bracts; sepals narrowly elliptic; petals linear; carpels 6, fused; styles 6, bifid. Fruit irregularly dehiscent. Seeds few.
Rhizome at least 1 cm thick, covered with persistent black, fibrous strands. Roots cord-like. Leaves 1.25-1.75 cm wide. Dioecious. Flowers with 3 petals and 3 sepals. Male spathe with numerous flower buds which become detached just before flowering, the flowers then freely floating on the surface. Female spathe with only one flower on a very long peduncle which contracts spirally after anthesis. Fruit densely set with erect bifid appendages
