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DescriptionUnarmed aquatic herb. Stems creeping, usually floating, and swollen. Leaves 2-pinnate, very sensitive. Inflorescences solitary, axillary, of spherical to ellipsoid heads. Flowers of 2 types: bisexual in upper part of the head; neuter with elongate staminodes in lower part. Calyx 5-toothed. Petals 5. Stamens 5 or 10. Pods clustered, oblong to subcircular, dehiscent. Seeds smooth, ± flattened.