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 The tallest "S. aucuparia" in the United Kingdom stands in the Chiltern Hills in South East England. This exceptional specimen is 28 m tall and has a trunk diameter of 56 cm. In Germany, an unusually large specimen is located near Wendisch Waren, a village in Mecklenburg-Vorpommern. This tree stands at more than 15 m tall, is around 100 years old, and has a diameter of 70 cm. The tallest known "S. aucuparia" in Ireland is an 18 m tall specimen at Glenstal Abbey, County Limerick. "Sorbus aucuparia" is pollinated by bees and flies. Its seeds are not digested by