prickly herbs with thick rootstocks. Leaves orbicular, floating. Flowers
partially submerged, epigynous. Sepals 4, inserted on the edge of the torus
above the carpels. Petals numerous in 3-5 whorls. Stamens numerous,
many-seriate, fascicled in bunches, filaments linear. Ovary 5-many celled with
a cup-like depression above formed by the radiating stigmas, ovules 2-3 in each
locule. Berry spongy, crowned by the persistent sepals and covered with stout
prickles. Seeds many with pulpy aril.