Rhizomes mostly 5-10 cm diam. Leaves mostly emersed, occasionally floating or submersed; petiole terete or adaxially slightly flattened. Leaf blade abaxially and adaxially green, broadly ovate to nearly orbiculate, 12-40 - 7-30 cm, 1-2 times as long as wide, sinus 1/3-1/2 length of midrib, lobes overlapping to divergent, often forming angle of 90° or greater; surfaces abaxially glabrous to sparsely pubescent. Flowers to 4 cm diam.; sepals mostly 6, abaxially green to adaxially yellow, rarely red-tinged toward base; petals oblong, thick; anthers 3-7 mm, longer than filaments. Fruit green, ovoid, 2-5 × 2-5 cm, moderately ribbed, slightly constricted below stigmatic disk; stigmatic disk green, occasionally reddened, 13-25 mm diam., entire to crenate; stigmatic rays 9-23, linear to lanceolate, terminating 1-3 mm from margin of disk. Seeds 3-6 mm. Flowering mid spring-early fall, extended farther south. Ponds, lakes, sluggish streams and rivers, springs, marshes, ditches, canals, sloughs, and tidal waters; 0-450 m; Ont.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Kans., Ky., La., Maine, Md., Mich., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico (Coahuila, Tamaulipas); West Indies (Cuba). Nuphar advena is extremely variable and intergrades with N . orbiculata , N . ulvacea , and N . sagittifolia in areas of sympatry. Intergradation with N . variegata (E. O. Beal 1956) can be observed in the mid-Atlantic region, although most floristic treatments from the area of overlap treat the two taxa as distinct species. Local variation in the Ozark Mountains and in Texas, the basis for the names Nymphaea ozarkana , N . ovata , and N . puberula , is not considered sufficient to warrant recognition.
Floating and submersed lvs rarely present; emersed lvs mostly 2-4 dm, on stout petioles, the subacute basal lobes separated by a broadly triangular sinus; petioles terete, or oval in cross section; fls 3-5 cm thick; sep 6, yellow within or rarely suffused with purple; anthers 3-7 mm, longer than the filaments; stigmatic disk greenish, 10-15 mm wide at anthesis, mostly 14-18-rayed; fr broadly ovoid, 4 cm, mostly thicker than long. Sluggish streams, less often in ponds; s. Me. to Fla. and Cuba, w. to Wis., Mo., Kans., Tex., and n. Mex. Summer. (N. fluviatilis; N. macrophylla; N. puteorum)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.