Aquatic perennials of fresh water; dioecious or hermaphrodite. Leaves all basal; juvenile submersed, ribbon-like with short petioles; older leaves with broad-ovate to suborbicular floating lamina, nerves 3-11, connected by fine parallel cross-veinlets, long-petiolate. Inflorescence scapose; spathes elliptic or ovate, often ribbed or winged, = or < perianth-tube, in male plants subtending many flowers, in female and bisexual plants subtending only one flower. Flowers with 3 green persistent sepals, 3 longer white petals. Male flowers pedicellate, stamens 6-15, ovary rudimentary; female flowers sessile, staminodia present or 0, ovary oblong, stigmas (3)-6-(9), bifid, ovules many; bisexual flowers with 6 or more stamens, 6 or more stigmas. Fruit a capsule ripening inside spathe. Seeds many. Spp. c. 40, mostly tropical, of Africa, S.E. Asia, Korea and Japan, Malaysia, Australia, New Caledonia and 1 sp. in S. America. Adventive sp.1.