Perennial aquatic herbs, floating or loosely anchored. Leaves submerged or partly emersed; petioles up to 60 cm. depending on the depth of the water, terete; leaf-blade linear to linear-lanceolate, much shorter than the petioles. Peduncles shorter than the leaves; inflorescence emersed, spicate, of unbranched whorls of sessile or subsessile flowers; upper whorls of ♂ flowers, lower of ♀ flowers; vegetative buds sometimes present in the lower whorls; bracts 3, connate. Male flowers: 4–8 flowers in each whorl, shortly pedicellate; bracteoles ovate; sepals 3, ovate; petals 0–3, much smaller than the sepals, membranous; stamens 3, filaments flattened; abortive carpels 2 or 3. Female flowers: 3 to each whorl, ebracteolate; sepals 3, ovate; petals 0–3, very small, membranous; staminodes 3; carpels 3–6, free; styles terminal; stigmas papillose, ovules solitary, basal; achenes ovate, swollen, with lateral air-chambers when mature, beaked with the remains of the style, smooth or ridged.
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