Syst. Nat. 2: 54. 1821.
Rhizomes unbranched, erect, ovoid; stolons absent. Leaves: petiole glabrous. Leaf blade abaxially purple, often spotted, adaxially green, ovate to nearly orbiculate, 15-45 × 15-45 cm, margins dentate to spinose-dentate; venation radiate and prominent centrally, without weblike pattern, principal veins 13-29; surfaces glabrous. Flowers emersed, 7-18 cm diam., opening and closing diurnally, only sepals and outermost petals in distinct whorls of 4; sepals green, abaxially flecked with short dark streaks, faintly veined, lines of insertion on receptacle not prominent; petals 12-21, white; stamens 50-190, yellow, outer with connective appendage projecting 3-10 mm beyond anther; filaments widest at or below middle, mostly equal to or shorter than anthers; pistil 14-25-locular, appendages at margin of stigmatic disk short-triangular, to 3 mm. Seeds nearly globose to ellipsoid, 1.2-1.6 × 0.9-1.3 mm, 1.2-1.5 times as long as broad, with longitudinal rows of hairlike papillae 40-180 µm.
Phenology: Flowering all year.
Habitat: Ditches, canals, ponds, and freshwater tidal margins
Elevation: 0-350 m
Fla., Tex., Mexico, West Indies, Central America, South America.
Reports of Nymphaea ampla in southern Texas by H. S. Conard (1905) are confirmed by specimens although no recent collections have been seen.