The Isle of Arran in Ayrshire, often called 'Scotland in miniature' for its varied scenery, quietly harbours one of Britain's rarest trees, the Arran Whitebeam. In Scottish Gaelic the species is known as Gall-uinnsean Arainneach.

Endemic to Scotland and classified as vulnerable, found wild only in northern Arran, with about 400 trees across 13 sites, from the coast up into the hills, sheltering from wind and sheep in deep gullies to 346m. Though very rare, it is one of the easier rare whitebeam hybrids to find, with a stronghold in Glen Catacol and a roadside 'Sorbetum' enclosure containing it and the related Arran Service-tree.

Syn. *Sorbus arranensis*. An apomictic triploid evolved from Rowan (p. xxx) and Rock Whitebeam (p. xxx). Considered to be quite long-lived among related species, with specimens known to live at least 120 years.

Small (4-6m), almost bush-like, often stunted and multi-stemmed from exposure and browsing. Bark grey-brown. Branches erect, rarely root-suckering. Buds lanceoloid, pointed, sparsely haired. Leaves elliptic-ovate to obovate, 5-9cm, pinnatilobate with rounded tips cut deeply (to 85 per cent of the way to the midrib), usually without fully free leaflets, dark green above, green-white downy below, with 13-18 veins, on an 8-20mm petiole. Flowers white in a 6cm inflorescence (June-July). Fruit a subglobose red pome (9-11mm). Arran Service-tree differs: pinched free basal leaflets.

Conservation efforts are underway, led by Glasgow Botanic Gardens and Royal Botanic Garden Edinburgh with support from the private Dougarie Estate on the Isle of Arran.

Berries sustain birds in autumn. One ornithological study has shown that birds preferentially feed on Rowan pomes before those of Arran Whitebeam.

Browsing by Red Deer (Cervus elaphus) and sheep are major threats. Even partially effective fenced exclosures seem to have been effective in encouraging natural regeneration and survival. Heavy snow and rockfalls can damage trees.

In a world where halting biodiversity decline is a major conservation goal, and given that Britain is one of the most nature-depleted countries, our credibility is on the line if we fail to conserve a single rare species that epitomises this country's wonderful natural history.