118 Potamogeton perfoliatus L.

This polymorphic species is widely distributed in Eurasia and N. America. Subsp. perfoliatus occurs through large parts of Eurasia, subsp. richardsonii (Benn.) Hult. through most of N. America and subsp. bupleuroides (Fem.) Hult. in eastern N. America. The species belongs to the circumpolar plants (Hultén, Circumpol. I, p. 182 and map 172).