Perennial aquatic herbs, rooted or free-floating. Leaves emergent (in ours), floating or submerged; petiole sometimes markedly swollen; lamina linear in some submerged forms, otherwise ovate to ± circular. Flowers 1-several-flowered racemes or spikes. Perianth funnel-shaped, zygomorphic, with a ± curved tube and 6 subequal spreading lobes. Stamens 6. Ovary 3-locular; ovules numerous. Capsule fusiform, covered with withering and persistent perianth. Seeds numerous, small, finely ribbed.