Variation in Two Sorbus Species Endemic to the Isle of Arran, Scotland

A study of the morphology of plants from four species of Sorbus, S. arraensis, S. pseudofennica, S. aucuparia and S. rupicola, two of them endemic to North Arran, suggested that the origin of the two endemic groups could have been by hybridization. Variation between individuals within the hybrid groups indicates that the two groups, probably of hybrid origin (S. arranensis and S. pseudofennica), could each consist of a set of genetically isolated clones reproducing by apomixis, with the possibility in the case of S. pseudofennica of occasional genetic interchange by sexual reproduction. The overlap of characters between the two hybrid groups suggests that the inflow of genetic material by hybridization and genetic modification in these groups is continuing.