Genetic diversity and differentiation of allopolyploid Dactylorhiza (Orchidaceae) with particular focus on the Dactylorhiza majalis ssp traunsteineri/lapponica complex

Genetic differentiation of Dactylorhiza majalis ssp. traunsteineri from the Alps, Scandinavia, and Britain was studied and compared with other allotetraploid members of the systematically challenging genus Dactylorhiza. One-hundred and eleven populations from altogether 18 taxa were analysed for eight polymorphic plastid markers and two size-variable fragments from the nuclear internal transcribed spacer (ITS) region. In total, 60 plastid haplotypes and six ITS alleles were found among the 737 individuals analysed. No clear differentiation between populations of ssp. traunsteineri from the three regions was revealed. However, ssp. traunsteineri was genetically differentiated from Dactylorhiza baumanniana, Dactylorhiza elata, and D. majalis ssp. sphagnicola, although the majority of allotetraploid taxa remained inseparable. Judging from the degree of concerted evolution in ITS, D. majalis ssp. alpestris may be regarded as a relatively old allotetraploid, whereas ssp. baltica and ssp. purpurella may be considerably younger. Based on plastid data, the Alp region had the highest genetic diversity followed by Scandinavia and Britain. The geographic distribution of haplotypes provided support for possible refugial areas around the Alps and for several independent immigration routes into Scandinavia after the last ice age. (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 52-67.