Rhizomes 2.5-7 cm diam. Leaves mostly floating, occasionally submersed; petiole adaxially flattened, with median ridge, winged along margins. Leaf blade abaxially and adaxially green, sometimes abaxially purple-tinged, broadly ovate to oblong, 7-35 5-25 cm, 1.2-1.6 times as long as wide, sinus 1/3-1/2 length of midrib, lobes approximate to overlapping; surfaces glabrous. Flowers 2.5-5 cm diam.; sepals mostly 6, abaxially green to yellow, adaxially usually with red or maroon toward base; petals oblong, thick; anthers 3-9 mm, longer than filaments. Fruit mostly purple-tinged, ovoid, 2-4.3 2-3.5 cm, strongly ribbed, slightly constricted below stigmatic disk; stigmatic disk green, rarely reddened, 8-20 mm diam., entire to deeply crenate; stigmatic rays 7-28, linear to narrowly lanceolate, terminating 0-1(-1.5) mm from margin of disk. Seeds 2.5-5 mm. 2 n = 34. Flowering late spring-summer. Ponds, lakes, sluggish streams, and ditches; 0-2000 m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Conn., Del., Idaho, Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Mont., Nebr., N.H., N.J., N.Y., N.Dak., Ohio, Pa., R.I., S.Dak., Vt., Wis. Nuphar variegata is distinct throughout most of its range. The leaves are characteristically floating, being emergent only under low-water conditions. Intermediates between N . variegata and N . microphylla , probably of hybrid origin, are treated as N . rubrodisca . Some intergrading of characteristics occurs where the range overlaps with N . advena (E. O. Beal 1956). This can be observed in the mid-Atlantic region. Intermediates between N . variegata and N . polysepala occur in eastern British Columbia where the two species are sympatric. Authorship and typification of this name were discussed by E. G. Voss (1965).
Durand Floating lvs 10-25 cm, two-thirds as wide, usually rounded above, the narrow basal sinus seldom over half as long as the midvein; submersed lvs few or none; petioles flattened on the upper side and narrowly winged; fls (2.5)3.5-5 cm thick, sep mostly 6, usually reddish within or on the basal half; anthers 4-7 mm, longer than the filaments; stigmatic disk green or greenish, 1 cm wide, mostly 10-15-rayed; fr ovoid, 2-4.5 cm, only slightly constricted below the disk; 2n=34. Ponds; Nf. to B.C., s. to Del., n. O., Io., Kans., and Ida. Summer. (N. fraterna)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.