Arran whitebeams complex fashion, which involved the common whitebeam ("Sorbus aria") giving rise to the tetraploid rock whitebeam ("Sorbus rupicola") which is still found on Holy Isle. This species is able to survive at higher altitudes and therefore occupies a less competitive niche with fewer tree species able to tolerate the harsher conditions. The rock whitebeam interbred with the rowan / mountain ash ("Sorbus aucuparia") to produce the hybrid, a fertile separate species the Scottish whitebeam ("Sorbus arranesis") which grows well in this zone of reduced competitive growth at higher altitudes. The bastard mountain ash ("Sorbus pseudofennica") arose from a further cross
Sorbus aucuparia larger forest trees. In Central Europe it often grows in association with red elderberry, goat willow, Eurasian aspen, and silver birch. The plant is highly flammable and tends not to accumulate plant litter. Other species of the genus "Sorbus" easily hybridize with "S. aucuparia" and hybrid speciation can result; hybrids include "Sorbus × hybrida", a small tree with oval serrated leaves and 2 to 3 pairs of leaflets, which is a hybrid with "Sorbus × intermedia", and "Sorbus thuringiaca", a medium-size tree with elongated leaves and 1 to 3 pairs of leaflets that are sometimes fused at the central vein,