Dioecious, submerged, freshwater, perennial herbs. Roots simple, adventitious, without root hairs, arising from nodes. Stems elongate, stoloniferous or erect, filiform to terete, simple or branched from axils; branches 1 per axil. Leaves sessile, spirally arranged, subopposite or in whorls, linear to lanceolate, shortly acuminate to subobtuse, patent to strongly recurved, firm or flaccid, with 2 apical spines, often with 2 bands of sclerenchyma fibres on either side of midrib and 2–6 rows of submarginal sclerenchyma fibres; venation reduced to midrib only; margins green or hyaline, denticulate. Stipules 0. Nodal scales 2 per leaf, linear to widely ovate, with entire or papillose margins. Flowers unisexual. Male spathe solitary in leaf-axil, sessile, ovate to suborbicular, toothed, containing up to 40 flowers. Male flowers shortly pedicellate, becoming detached and floating before anthesis; sepals and petals 3, oblong-ovate to ovate, obtuse or cucullate, usually reflexed at anthesis; stamens 3; anthers 4-thecous, fixed at right-angles to the filaments; filaments filiform, spreading horizontally; staminodes often present, 3, filiform, papillose, longer than the stamens, usually joined at the apex and functioning as a sail. Female spathe solitary in leaf-axil, sessile, narrowly ovate to ovate, toothed, 1-flowered. Female flower: sepals and petals 3, elliptic to ovate, obtuse or cucullate, usually reflexed at anthesis; staminodes 3, minute, linear; ovary 1-locular, placentation parietal; ovules 5–30, orthotropus; perianth-tube filiform, exerted laterally from the ovary near apex of the spathe, carrying perianth to the water surface; styles 3; stigmas 6, 2 per style, linear, papillose. Fruit ovate, beaked at apex, pericarp smooth, irregularly dehiscent. Seeds narrowly ellipsoid to ellipsoid, smooth, with short stipe at base, attenuate at apex.
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Vigorous, submersed, aquatic perennials of fresh water; dioecious. Stems ± branched, leafy throughout. Leaves numerous, sessile, minutely toothed, alternate, subopposite or whorled. Spathes solitary, axillary; in male plant enclosing many pedicellate flowers; in female plant enclosing 1-(2-3) sessile flowers; male flowers usually breaking off and floating within a bell formed by recurved perianth-segments; female flowers long-exserted on pedicel-like extension of perianth-tube and reaching surface of water. Perianth of 6 segments. Male flowers; stamens 3, staminodia 3, > stamens, coloured at top and joined forming a sail. Female flowers: staminodia 3, small, stigmas 3, bifid, often brightly coloured. Fruit a beaked capsule, becoming mucilaginous and bursting irregularly. Seeds many. Spp. c. 15, of tropical and S. Africa, Madagascar and India. Adventive sp. 1.
Freshwater, dioecious, perennial aquatic, attached or free-floating. Leaves submerged, cauline, ±alternate, irregularly arranged or rarely whorled, not differentiated into blade and sheath, with midrib; margins toothed or entire. Inflorescences floating, axillary, solitary. Flowers with perianth of 2 ±similar whorls, the inner segments slightly broader. Male flowers numerous in spathe, separating when in bud and rising to water surface, opening when free-floating; stamens 3; staminodes 3, larger than stamens and functioning as sails. Female flowers 1–3 per spathe; hypanthium thread-like; staminodes 3; ovary unilocular; styles 3, bifid. Fruit capsular. Seeds numerous.
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