Bot. Gaz. 11: 167. 1886 (as rubrodiscum).
Rhizomes 1-2.5(-4) cm diam. Leaves mostly floating, occasionally submersed; petiole flattened. Leaf blade often abaxially purple on new leaves, adaxially green to greenish purple, broadly ovate to oblong, 5-25 × 4.5-15 cm, 1.1-1.7 times as long as wide, sinus ca. 1/2 length of midrib, lobes overlapping to divergent and forming V-shaped angle; surfaces glabrous. Flowers 3 cm or more diam.; sepals 5-6, abaxially green to yellow, adaxially often red-tinged toward base; petals broadly spatulate and thin, or notched and thickened; anthers (2-)3-6 mm, shorter than filaments. Fruit purple, dark brown, or rarely green, globose-ovoid, occasionally flask-shaped, 1.5-2.5 cm, strongly ribbed, deeply constricted below stigmatic disk, constriction 5-10 mm diam.; stigmatic disk red, 8-14 mm diam., with 8-14 shallow crenations; stigmatic rays 8-15, linear, terminating 0-1.6 mm from margin of disk. Seeds 2.5-3.5 mm.
Phenology: Flowering summer.
Habitat: Ponds, lakes, sluggish streams, sloughs, and occasionally tidal waters
Elevation: 0-400 m
N.B., N.S., Ont., Que., Conn., Maine, Mass., Mich., Minn., N.H., N.J., N.Y., Pa., Vt., Wis.
Nuphar rubrodisca is generally considered to be a hybrid between N. microphylla and N. variegata because it displays characteristics intermediate between the two taxa. It is reportedly sterile in some areas and completely fertile in others.