What is the origin of the Scottish populations of the European endemicCherleria sedoides(Caryophyllaceae)?

Cherleria sedoides L. (Minuartia sedoides (L.) Hiern) is a montane perennial which, with some species in Minuartia sect. Spectabiles, is more closely related to Scleranthus than to other Minuartia species and is therefore best restored to the reinstated and redefined genus Cherleria. Reconstruction of the ancestral area of the clade containing C. sedoides suggests that it evolved in the Alps or the Balkan peninsula. The species now has an unusual distribution, being present in the mountains of southern Europe and Scotland but absent from the Arctic. Three historical scenarios that might have led to the presence of the species in Scotland are outlined and tested by a molecular analysis comparing Scottish populations with populations from the Pyrenees and the Alps. The sampled populations show little variation in internal transcribed spacer (ITS)/external transcribed spacer (ETS) but much more in cpDNA. The latter reveals a major division between some Alpine material and the other Alpine, Pyrenean and Scottish plants. Once the anomalous Alpine haplotypes are excluded, Scottish populations are at least as variable as those from the Alps and Pyrenees, and are closely related to both. We conclude that they have not undergone a long period of isolation, nor have they originated by recent, long-distance dispersal from the Alps or Pyrenees. They appear to be derived from a metapopulation that was probably widespread at the last glacial maximum (LGM) and gave rise to the Alpine, Pyrenean and Scottish plants.