| Betula pubescens subsp. tortuosa (Ledeb.) Nyman | |
| Publ. & Syn. | ?Betula czerepanovii N.I. Orlova, Vestn. Leningradsk. Univ., Ser. Biol. 1978, 3: 60 (1978). Holotype (LE): European Russia: the Murman area, "Paeninsula Kolaënsis, montes Chibinenses, decline austro-occidentale montes Jukspor", 08. July 1947, leg. N.I. Orlova. - ?Betula pubescens subsp. czerepanovii (N.I. Orlova) Hämet-Ahti, Phytocoenologia 15: 450 (1987). |
| Notes | The Fennoscandian "Mountain birch" has been interpreted as a hybrid product from introgression of the diploid Betula nana into the tetraploid B. pubescens (subsp. pubescens) through the triploid fertile hybrid. Note that the real ploidy levels probably are tetra, hexa, and octoploid, explaining the fertility of the hybrid. This hypothesis finds some support in recent molecular studies (Järvinen et al. 2004; Eidesen 2007). Hybrids between B. nana and B. pubescens subsp. tortuosa are common throughout Fennoscandia. Hybridization has probably influenced large parts also of the Icelandic populations, due to the extensive anthropogenic impact where the more shrubby (and less useful) hybrids would be favoured as survivors in the human-run selection. There is a differentiation in the Icelandic population between the plants in the west and the east (J. Pálsson pers. comm., Elven and Solstad observ.). The eastern plants conform to the Fennoscandian ones, whereas the western plants are shrubby, with dark bark, and small, rounded and more round-dentate leaves, suggesting much more influence from B. nana than in the eastern plants. As long as subsp. tortuosa constitutes a recognizable entity, the influence of B. nana does not necessarily influence the taxonomy. However, there are doubts whether it is a consistent entity (see Jonsell 2000c). One should, however, note that it is present in at least one region where B. pubescens subsp. pubescens is absent (Iceland). However, in molecular data the Icelandic plants merge with the Scandinavian ones (Eidesen 2007). |
| Chromosomes | 56 (4x). - Europa (N), Siberia (N). - Several reports. |
| Geography | European (N) - Asian (N/C): ICE NOR RUS SIB. |
| Distribution | N = F D = ? Ic = f E = F YG = r FN = f UN = r Tm = r KP = s [ key ] |
| Parent taxon | Betula pubescens Ehrh. |
| PAF ID | 610206b |