Japan Flora: Rhizomes stout, creeping; floating leaves broadly ovate to ovate-orbicular, sometimes elliptic, 6-8 cm. long, 6-9 cm. wide, the petioles slightly flattened; flowers about 2.5 cm. across, yellow, floating; sepals broadly obovate or broadly elliptic, 12-20 mm. long, rounded at apex; petals spathulate-obovate, 5-7 mm. long, rounded at apex, often obsoletely toothed; andiers elliptic, 2.5-3 mm. long; stigma-disc 6-8 mm. across, pale yellow or partially reddish; stigma-disc 10-20 mm. across. July-Aug. Ponds and shallow lakes. 

Hokkaido (e. distr.), Honshu (n. distr.). Europe to Siberia.

var. ozeense (Miki) Hara. With dark red stigma-disc. Honshu (Oze in Kotsuke).