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
Mountain Ash, Rhondda Cynon Taf the Aberdare branch of the Merthyr Line of the Transport for Wales rail network. Further to Mountain Ash railway station, the village of Fernhill and Penrhiwceiber is also served by the Aberdare line. Bus services are operated by Stagecoach in South Wales. An early British railway line had developed from the industrial development within the South Wales Valleys, which with its core centred around Mountain Ash became known as the Mountain Ash Railway (MAR). Having developed from an early tramway, it became in the 1970s the last core of steam locomotive operations in the UK. Developed by Powell Duffryn as