622 Betula nana L.

This widespread species is divided into two subspecies, viz. subsp. nana (Europe and W. Siberia) and subsp. exilis (Suk.) Hult. (C. and E. Siberia and N. America). The distribution in N. America of subsp. exilis is recorded differently by Meusel et al. 1965, map p. 119, and Hultén, Fl. Alaska Neighbor. Terr., map p. 365. According to Hultén (I. cit.) "subsp. exilis forms complete introgression with B. glandulosa where ranges overlap", i. e. through the whole northern N. America. Both subsp. nana and subsp. exilis are reported from Greenland. Further, the more limited distribution areas of B. michauxii Spach (eastern N. America) and B. rotundifolia Spach (C. Asia) are mapped separately. B. nana coll. belongs to the circumpolar plants (Hultén, Circumpol. Il, p. 358 ff. and map 128). Cf. also Meusel et al. 1965, map p. 119.