Densely prickly annual or short lived perennial herbs with short, thick rhizome. Leaves floating, orbicular, corrugated. Flowers usually cleistogamoos, partially or entirely submerged, epigynous. Sepals 4, erect, persistent. Petals violet or red many in 3-6 series, shorter than the sepals. Stamens many, free; staminodes usually absent. Carpels usually variable in number without free appendages, ovary as many loculed as capels, ovules many on parietal placenta; stigmatic disc obconical. Fruit prickly, seeds 8-20 with pulpy aril, and thick testa.