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 which is a hybrid with "Sorbus aria". The main pests for "S. aucuparia" are the apple fruit moth "Argyresthia conjugella" and the mountain-ash sawfly "Hoplocampa alpina". The rust fungus "Gymnosporangium cornutum" produces leaf galls. The leaves are not palatable to insects, but are used by insect larvae, including by the moth "Venusia cambrica", the case-bearer moth "Coleophora anatipennella", and leaf miners of the genus "Stigmella". The snail "Helix aspersa" feeds on the leaves. The plant can suffer from fire blight. Fossils of "Sorbus aucuparia" have been described from the fossil flora of Kızılcahamam district in Turkey, which is of early