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 East Newtown, Caegarw, Cwmpennar and Cefnpennar. According to the 2011 UK Census Mountain Ash East had a population of 2,909. Mountain Ash East includes the village's Grade II listed St Margaret's Church, designed by John Pollard Seddon. An electoral ward of Mountain Ash East pre-existed the community. The ward elects one county councillor to Rhondda Cynon Taf County Borough Council. Since 1995 the ward has been represented on the council by Plaid Cymru councillor, Pauline Jarman, who was previously a councillor on Cynon Valley Borough Council. She first stood for election in 1976. Cllr Jarman has been leader of the Plaid