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
Aphis pomi "A. pomi", especially at high temperatures. Besides occurring on apple ("Malus domestica"), "Aphis pomi" infests other plants in the family Rosaceae including pear ("Pyrus communis "), hawthorn ("Crataegus monogyna"), medlar ("Mespilus germanica"), quince ("Cydonia oblonga"), mountain ash ("Sorbus aucuparia"), rose ("Rosa") and spiraea ("Spiraea"). It is an autoecious species, completing its life cycle on a single host species. Overwintering eggs hatch in spring and the aphids colonise the growing tips of the shoots causing the edges of the leaves to curl. These aphids are all viviparous females and give birth to other wingless aphids by parthenogenesis. In June some winged