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 alnifolia fruit (persistent in other whitebeams), but genetic evidence places it close to "Sorbus aria". It is occasionally grown as an ornamental tree in northern Europe, primarily for its autumn colour. The cultivar 'Skyline' has been selected for its fastigiate growth. Sorbus alnifolia Sorbus alnifolia (syn. "Aria alnifolia"), also called alder-leafed whitebeam, Korean whitebeam, or Korean mountain ash, , is a species of whitebeam native to eastern Asia in eastern and northern China, Taiwan, Korea and Japan. "Sorbus alnifolia" is a medium-sized deciduous tree growing to 10–20 m tall with a trunk up to 30 cm diameter and grey bark; the