619 Betula alba L., lowland taxa

The taxa belonging to the collective species B. alba L. (the arborescent birches) are here grouped in two categories, viz. lowland taxa (map 619) and subalpine and subarctic taxa (map 620). Map 619 thus illustrates the total range of B. verrucosa Ehrh. (syn.: B. pendula Roth) and B. pubescens Ehrh., although separately, together with some more or less closely related species, mainly in Asia and N. America. The taxonomical uncertainty in this intricate complex causes difficulties in drawing the distribution lines in several parts of the wide circumpolar range (cf. Hultén, Circumpol. Il, p. 90, 340-343). In addition, the occurrences can to a large extent be unevenly distributed, especially in cultivated areas. Cf. also Meusel et al. 1965, maps p. 118 and 119; Tolmachev, Atlas SSSR 1976, map 180-181; Porsild and Cody 1980, maps p. 258.