Rhizomes 3-8 cm diam. Leaves mostly floating, occasionally emersed or submersed; petiole terete. Leaf blade abaxially and adaxially green, widely ovate, 10-40(-45) × 7-30 cm, ca. 1.2-1.5 times as long as wide, sinus 1/3-2/3 length of midrib, lobes divergent to overlapping; surfaces glabrous. Flowers 5-10 cm diam.; sepals mostly (6-)9(-12), abaxially green to adaxially yellow, sometimes red-tinged toward base; petals oblong, thick; anthers 3.5-9 mm, slightly shorter than filaments. Fruit green to yellow, cylindric to ovoid, 4-6(-9) × 3.5-6 cm, strongly ribbed, slightly constricted below stigmatic disk; stigmatic disk green, 20-35 mm diam., entire to crenate; stigmatic rays 8-26(-36), linear to lanceolate, terminating within 1(-1.5) mm from margin of disk. Seeds 3.5-5 mm. 2 n = 34. Flowering spring (later in north)-summer. Ponds, lakes, and sluggish streams; 0-3700 m; B.C., N.W.T., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Mont., Nev., N.Mex., Oreg., Utah, Wash., Wyo. Plants intermediate between Nuphar polysepala and N . variegata occur in eastern British Columbia.
LEAVES: usually floating, sometimes emersed, broadly ovate to oblong, glabrous; petioles terete. FLOWERS: to 12 em in diameter when fully open; sepals 7-9(-12); petals small, usually concealed by the stamens, usually yellow, sometimes red-tinged; stamens with yellow to deeply red-tinged anthers, the filament often extending 1-4 mm beyond the anther; stigmatic disk entire to deeply crenate, usually deeply umbilicate, with (9-)20-25(-36) rays. SEEDS: narrowly ovoid, 2.5-3.2 mm wide and 3.5-5 mm long. NOTES: See the parent taxon for further description. Ponds, lakes and still to slow-moving water: Coconino, Navajo cos.; 2000-2250 m (6600-7500 ft); Apr-Sep (fr. Jun-Oct); Eurasia, but long-established in N. Amer.; Rocky Mt. region and w N. Amer.: AL and Yukon Terr. s to CA, AZ, and NM. Seeds and rhizomes a source of food. REFERENCES: Ricketson, Jon. 1995. Nymphaeaceae. J. Ariz. - Nev. Acad. Sci. 29(1). 26.