Perennial herbs with creeping rhizomes. Leaves radical with lamina float¬ing on the surface of water, borne on a long stalk, ovate to orbicular, entire, toothed or sinuate-toothed with a cordate or sagittate base. Flowers large, showy, floating or held above the water surface, borne on long pedicels, pedicels and petioles traversed by several longitudinal air cavities. Sepals 4, adnate to the base of. the torus, sometimes indistinguishable from petals. Petals many, of different colours, gradually transforming into stamens.
Stamens petaloid, anthers linear and introrse with or without appendages. Carpels many, in one whorl, usually with a sterile appendage on the outside of the stigmatic disc, ovary sunken in fleshy torus, with as many locules as carpels, stigmas many, concave, radiate. Fruit a spongy berry-l ike, usually ripening under water. Seeds many, enclosed in a transparent saccate aril, floating for sometime.
A genus with c. 50 species, almost cosmopolitan, distributed in tropical and temperate regions of the world. Represented in Pakistan by 5 species.
The species of the subgenus Castalia DC. are interfertile. This may account for intermediates and variability of different species particularly in Nymphaea alba L, Nymphaea candida C. Presl and Nymphaea tetragona Georgi complex.