610206-07 The Betula pubescens aggregate B. minor, B. pubescens
Geography: Amphi-Atlantic - European - Asian (W).
Notes: Betula pubescens s. lat. is tetraploid (2n = 56) and has been considered a broadly amphi-Atlantic complex distributed under partly different names from northeastern Canada over Greenland and Iceland to mainland northern Europe, western Siberia, and probably to central Asia. It may, however, be problematic to include the Canadian-Greenlandic plants and the European ones in the same species.
Löve and Löve (1975a) recognized seven subspecies from the Arctic (in their wider concept of the Arctic): subsp. borealis subsp. [minor?] in northeastern Canada and Greenland, the others in Eurasia. Of the Eurasian races, the lowland subsp. pubescens reaches the Arctic in northeastern European Russia and the Polar Ural (Orlova 1976; Jalas and Suominen 1976) and perhaps in northwestern Siberia. Four of the races recognized by the Löves were described on material from Fennoscandia: subsp. callosa, subsp. concinna, subsp. coriacea, and subsp. subarctica. See Øvstedal (1993) for an efficient refutation of B. callosa as a taxon. Betula concinna and B. coriacea were both described from within the range of B. pubescens subsp. pubescens and were synonymized with it by Jonsell (2000c). Subspecies subarctica may be a hybrid. None of these are currently accepted by Nordic authors, see, e.g., Jonsell (2000c) who discussed the variation but did not accept any races in northern European B. pubescens.
Czerepanov (1966) recognized four species for the European parts of arctic Russia: B. callosa in the Murman area, perhaps also farther east at the Jenisei; B. pubescens in the Pechora area, Bolshezemelskaya Tundra, Polar Ural, and perhaps also farther east; B. subarctica in the Murman area; and B. tortuosa from the Murman area to the Jenisei and south to the Altai.
The last-mentioned name, "tortuosa", is the one that for a long time most frequently has been applied to the mountain birch of Fennoscandia, Iceland, and Greenland (e.g., Hultén 1958; Löve 1970a; Feilberg 1984a; Walters 1993; Stace 1997; Elven et al. 2005). As this name is based on plants from the Altai, several authors have assumed that the name "tortuosa" has been misapplied to the European plant (Orlova 1978; Hämet-Ahti 1987). The Fennoscandian "Mountain birch" has been considered to be restricted to the surroundings of the North Atlantic, very far from the Altai. Several authors have therefore in recent years replaced the name "tortuosa" by subsp. czerepanovii or B. czerepanovii for the Fennoscandian mountain plants (e.g., Hämet-Ahti 1987; Elven 1994; Hämet-Ahti et al. 1998; Sekretareva 1999, 2004), but that name may rather relate to some hybrid. Walters (1993) and some Nordic authors have proposed to apply the name subsp. carpatica, based on a central European subalpine plant, to the Nordic mountain plants. This proposal has some molecular support and may be the future solution.
Tzvelev in comment 2000 stated that he had compared the northern European plants with the type of subsp. tortuosa and concluded that they could be merged. This means that the long applied name "tortuosa" could be re-instated but that the range of the taxon must be extended to include the northern and central Asian upland areas and probably also the area of subsp. carpatica. If so, the name subsp. tortuosa has priority before subsp. carpatica. However, Tzvelev (2002) had changed his opinion and excluded "tortuosa" as a relevant name for European birches. We do not know his arguments for this.
We provisionally accept three taxa from the Arctic: the eastern Canadian and Greenlandic plants as B. minor, the lowland European-Siberian plants as B. pubescens subsp. pubescens, and the Icelandic, Fennoscandian, northern Russian, and northern Siberian plants tentatively as B. pubescens subsp. tortuosa.
- Betula [6102,genus]