Taxonomy of Betula

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Subgenus Betulenta - Wintergreen oil birches[edit]

Bark on twigs rich in methyl salicylate (oil of wintergreen). Female catkins erect.

Subgenus Betulaster - Large-leaf birches[edit]

Bark on twigs contains some methyl salicylate. Female catkins pendulous.

Subgenus Neurobetula - Costate birches[edit]

Bark on twigs without methyl salicylate. Female catkins erect.

Subgenus Betula - Typical birches[edit]

Bark on twigs without methyl salicylate. Female catkins pendulous.

Subgenus Chamaebetula - Dwarf birches[edit]

Small shrubs with small rounded leaves. Female catkins pendulous.

Notes[edit]

There is no consensus at all on species limits in Betula, with different authors differing wildly in what species they accept, from under 30 species, to over 60. The above (incomplete) list was compiled from the references cited below. Birches will hybridise very freely, particularly in cultivation but also in the wild where conditions and species present permit. While differing chromosome number (diploid, tetraploid, etc.) may reduce interbreeding, it is not an absolute bar to it. Many botanists regard differing chromosome number as a specific discriminant, though not all do so (e.g. some include B. cordifolia and B. neoalaskana as varieties within B. papyrifera).

References[edit]

  1. ^ Wolfe, Jack A. & Wehr, Wesley C. 1987. Middle Eocene Dicotyledonous Plants from Republic, Northeastern Washington. United States Geological Survey Bulletin 1597:13
  2. ^ Crane P.R. & Stockey R.A. 1987; "Betula leaves and reproductive structures from the Middle Eocene of British Columbia, Canada." Canadian Journal of Botany 65(12): 2490-2500.
  • Bean, W. J. 1976, 1988. Trees & Shrubs hardy in the British Isles. Eighth edition, revised, vol. 1 (1976) & Supplement (1988); editor D. L. Clarke.
  • Hunt, D. 1993. Betula. Proceedings of the IDS Betula Symposium 2-4 October 1992. International Dendrology Society.
  • Li, J., Shoup, S. & Chen, Z.; Shoup, Suzanne; Chen, Zhiduan (2007). "Phylogenetic Relationships of Diploid Species of Betula (Betulaceae) Inferred from DNA Sequences of Nuclear Nitrate Reductase". Systematic Botany 32 (2): 357–365. doi:10.1600/036364407781179699. 
  • Rushforth, K. D. 1999. Trees of Britain & Europe. Collins. (Useful details on chromosome numbers of many European & Asian birches).
  • Skvortsov, A. K. 2002. A new system of the genus Betula. Byulleten Moskovoskogo Obshchestva Ispytatelei Prirody Otdel Biologie 107: 73–76.
  • Flora of North America online - Betula.
  • Grimshaw, J. 2009, New Trees, Recent introductions to cultivation. Kew Publishing

See also[edit]