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Robust aquatic herbs, with vegetative rhizomes and thickened storage rhizomes. Leaves arising directly from rhizome, floating, raised above water surface and submerged; lamina peltate, orbicular; submerged leaves ± lanceolate. Flowers bisexual, actinomorphic, solitary, axillary, raised above water surface. Perianth segments c. 14–30, 2–5 outermost ones sepaloid, remainder petaloid. Stamens c. 200–400; filaments elongate; anthers with 4 pollen sacs; connective prolonged, conspicuous. Carpels c. 9–40 borne singly in, but free from, cavities in pithy obconical receptacle, with only styles and stigmas protruding; styles very short; ovule solitary, anatropous, pendulous from top of ovule. Fruits separate, hard-walled nuts loose in cavities in greatly enlarged receptacle; each nut with small respiratory pore at top. Seed solitary.
Herbs perennial, aquatic. Rhizomes branched, repent, forming swollen terminal storage tubers late in growing season. Leaves arising from rhizome, alternate, emersed or floating, long petiolate; leaf blade centrally peltate, veins radially extended. Flowers solitary, axillary, long pedunculate, bisexual, hypogynous, actinomorphic, entomophilous, borne above water surface. Tepals numerous, distinct, outermost reduced, inner ones larger and petaloid. Stamens numerous; anthers dehiscent by longitudinal slits. Pistils numerous, simple, separately and loosely embedded in cavities on flattened top of receptacle. Ovary 1-loculed; ovule 1, pendulous; styles very short; stigmas capitate. Fruit nutlike, indehiscent. Seeds without endosperm and perisperm; embryo large; cotyledons 2, fleshy.
