Leaves wholly submerged; petioles varying greatly in length according to depth of water; leaf blades varying greatly in shape and size, linear to broadly cordate, base cordate to attenuate, margin entire, undulate, or serrulate, apex obtuse. Flowers unisexual. Spathe with 2-6 longitudinal ribs. Male spathe with 40-190 male flowers; sepals green; petals white with yellow base, obcordate or obovate, 1-3.5 cm; stamens 9-12; filaments hairy; anthers ovoid-elliptic; staminodes 3. Female spathe with 2-9 female flowers; perianth similar to male ones; ovary triangular-cylindric with 3 carpels; styles 3, deeply bifid; staminodes 3. Fruit triangular-cylindric to fusiform, ca. 8 cm. Seeds narrowly elliptic, with or without hairs. Fl. May-Oct. 2n = 22*.