620 Betula alba L., subalpine and subarctic taxa

The N. European and W. Siberian B. tortuosa Ledeb., generally considered as a subspecies, variety or forma of B. pubescens Ehrh., is mapped together with some other more or less closely related species (or subspecies) in other mountain areas of Eurasia and N. America. To a large extent the distribution lines are generalized and tentatively drawn (as on map no. 619). Altogether these subalpine and subarctic taxa have a circumpolar distribution (Hultén, Circumpol. Il, map 82). Cf. also Meusel et al. 1965, map p. 119.