Pistia

Free-floating aquatic, acaulescent, rosulate, herb with pendulous fibrous roots. Leaves subsessile, densely pubescent; lamina with parallel primary veins. Inflorescence hidden among leaf bases. Spathe constricted in the middle; basal part slightly inflated, convolute; apical part ± erect, expanded. Spadix highly reduced, adnate to spathe. Flowers unisexual; perianth segments 0. Male flowers 2-8, connate into a single whorl borne on a short stipe, subtended by a basal cup. Female flowers solitary; basal part consisting of a single 1-locular ovary; ovules numerous; style curved. Fruit a several-seeded berry, dehiscing by irregular splits. Seeds subcylindric, rugose.