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 secondary school is the hospital Ysbyty Cwm Cynon which opened in 2012 replacing the old Mountain Ash General Hospital. Local primary schools include Our Lady's R.C Primary School, Caegarw Primary School (Ysgol Gynradd Caegarw), Glenboi Primary School (Ysgol Gynradd Glen-boi), Darranlas Primary School (Ysgol Gynradd Darren-las), Miskin Primary School (Ysgol Gynradd Meisgyn), Penguelan Primary School (Ysgol Gynradd Pengeulan) and Penrhiwceiber Primary School (Ysgol Gynradd Penrhiwceibr). Mountain Ash has a rugby union team called Mountain Ash RFC. Rugby league club South Wales Scorpions also currently play their home matches in Mountain Ash. Nos Galan (), is an annual running road race,