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 randaiensis Sorbus randaiensis Sorbus randaiensis is a deciduous tree of family Rosaceae. It is an endemic species in Taiwan and can be found in the mountain areas of middle Taiwan, with altitude 1,800m to 3,200m, mostly spotted in the forest of Xueshan, Hehuan Mountain, , and Nenggao Mountain. It is a tree 3–8 m tall with white flowers and reddish fruit. Koidz., The Journal of the College of Science, Imperial University of Tokyo, Japan 34(2): 52. 1913. (J. Coll. Sci. Univ. Tokyo) Its species epithet "randaiensis" implies that the first type specimen was collected at Randaien Mountain, and to some degree