Aquatic, annual or perennial, with emergent leaves and inflorescences. Juvenile leaves submerged, linear; mature leaves with petioles sheathed at base; blade sagittate, with obtuse apex. Inflorescence with up to 8 whorls of flowers; lower 1 (or 2) whorl(s) bisexual with either female or bisexual flowers and sometimes also with male flowers, the lower whorl(s) opening and maturing first, the peduncle then bending towards the water until nutlets contact water surface; upper whorls of male flowers forming tip of inflorescence which turns upwards as male flowers open; branches and pedicels bracteate, the bracts maroon. Fruiting pedicels at first reflexed then thickening and elongating geotropically. Sepals 3, green. Petals 3, cream or greenish, constricted at base. Stamens 6, maroon. Carpels 5–15, in several whorls. Achenes crowded, few, swollen, spinescent when mature, with spines to 5 mm long; lateral air chambers absent.
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