The Arran whitebeams are species of whitebeam endemic to the island of Arran, Ayrshire, Scotland. Status These trees, sometimes called the Scottish or Arran whitebeam (Sorbus arranensis), the bastard mountain ash or cut-leaved whitebeam (Sorbus pseudofennica) and the Catacol whitebeam (Sorbus pseudomeinichii) are, if rarity is measured by numbers alone, amongst the most endangered tree species in the world. They are protected in Glen Diomhan off Glen Catacol, which was formerly part of a National Nature Reserve; although this designation was removed in 2011 the area continues to form part of a designated Site of Special Scientific Interest (SSSI). Only 283 Arran whitebeam and 236 cut-leaved whitebeam were recorded as mature trees in 1980, and it is thought that grazing pressures and insect damage are preventing regeneration of the woodland. They are typically trees of the mountain slopes, close to the tree line. However, they will grow at lower altitudes, and they are being grown within the Brodick Country Park. Also, North Ayrshire Council Parks and Recreation staff are growing specimens for conservation purposes. A few specialist garden centres and tree nurseries are able to supply them as grafts, and Ardrossan Academy in North Ayrshire has a grafted specimen for its use within the Scottish Higher Biology course in which it features as an example of evolution and survival of the fittest. Distribution Sorbus arranensis: Abhainn Bheag (Uisge solus), Glen Diomhan (and tributary), Glen Catacol, Allt nan Calman, Allt Dubh, Gleann Easan Biorach and Glen Iorsa (Allt-nan-Champ). Sorbus pseudofennica: Abhainn Bheag (Uisge solus), Glen Diomhan and Allt nan Calma. Sorbus pseudomeinichii: Glen Catacol. History The oldest preserved specimen is from the bastard mountain ash, S. pseudofennica, collected in 1797 from North Arran and another of the same species is in the British Museum dated 1838, when it was known as Pyrus pinnatifida (the pear group). S. pseudofennica was authoritatively recognised as a separate species by Clapham, Tutin and Warburg in 1952. Landsborough in 1875 noted the two kinds growing in Glen Diomhan and called them French rowan or whitebeams. The Scottish mountain ash, S. arranensis, evoked most collecting interest in 1870–1890 and 1920–1940, although older herbarium specimens exist. Evolution The trees developed in a highly 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