Description

Unarmed 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.