Rhizomes 2-5 cm diam. Leaves floating or submersed; petiole terete. Leaf blade abaxially and adaxially green, lanceolate to ovate, 15-25 × 8-10 cm, ca. 2.5 times as long as wide, sinus less than 1/3 length of midrib, lobes often overlapping; surfaces glabrous. Flowers 2-3 cm diam.; sepals 6-9, abaxially green to adaxially yellow toward base; petals oblong, thick; anthers 2-5 mm, slightly longer than filaments. Fruit green, nearly globose, 1.5-2.5 × 1.5-2.5 cm, strongly ribbed, slightly constricted below stigmatic disk; stigmatic disk green, 11-18 mm diam., undulate; stigmatic rays 9-16, ± elliptic, terminating within 1 mm from margin of disk. Seeds 3.5-4 mm.

Flowering spring-early fall. Blackwater rivers and streams; of conservation concern; 0-100 m; Fla.

Nuphar ulvacea is probably better treated as a subspecies. Gulf coast plants intermediate between N . ulvacea and N . advena , which have been treated as Nymphaea [ Nuphar ] chartacea , are treated under N . advena .