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Whitebeam, Arran (Sorbus arranensis)

Rare, rugged, isolated. Arran whitebeam is one of the rarest and most endangered trees in the world. It is a hybrid of rowan and rock whitebeam which has stayed on the Isle of Arran since the last glaciers were formed.

Arran whitebeam is one of the most endangered trees in the world.

Credit: Alastair Hotchkiss / WTML

Its leaves are covered underneath with an uneven, grey-white felt.

Credit: Brian Legg / WTML

The tree is a hybrid of rowan and rock whitebeam.

Credit: FLPA / Alamy Stock Photo

Their leaves are a popular food choice for wild deer.

Credit: Royal Botanic Garden Edinburgh / WTML

The trees are confined to the northern end of the Isle of Arran in Scotland.

Credit: Alastair Hotchkiss / WTML

At the last count, only 407 of these trees were growing in the wild.

Credit: Alastair Hotchkiss / WTML

Quick facts

Common names: Arran whitebeam, Scottish whitebeam

Scientific name: Sorbus arranensis

Family: Rosaceae

Origin: native (endemic to the Isle of Arran)

The Arran whitebeam is a small, slender, broadleaf tree only found naturally on the Isle of Arran in Scotland. In favourable, sheltered conditions it can reach a height of 7.5m, but many of the trees don’t grow above 2m because of the harsh weather conditions and over-grazing. Those stunted, often multi-stemmed specimens produce neither flowers nor fruit.

Look out for: the leaves which share some of the characteristics of both rowan (Sorbus aucuparia) and rock whitebeam (Sorbus rupicola), the original parent species. The rock whitebeam has no lobes, the rowan has pronounced leaflets (separate leaves on the leaf stem) and Arran whitebeam has lobes but not separate leaflets.

Its leaves are pinnately lobed to varying degrees.

Credit: FLPA / Alamy Stock Photo

What does Arran whitebeam look like?

Leaves

Green and pinnately lobed to varying degrees but rarely with any leaflets. They are broadest in the middle and covered underneath with an uneven, grey-white felt.

Flowers

8–10mm in diameter with cream petals are produced in May to early June. They are grouped in clusters and hang from the branches.

Fruits

Resemble those of the common whitebeam. They are small – 8-10mm, longer than they are broad – red-orange berries that hang in clusters.

Credit: Alastair Hotchkiss / WTML

Where to find Arran whitebeam

At last count, there were only 407 trees growing in the wild, and all of these are on the Isle of Arran in Scotland. It prefers acidic soils, and individual trees grow in small pockets of remnant woodland on rocky crags and steep-sided slopes. The trees are now confined to the northern end of the island and are mostly found in two Arran glens: Glen Catacol and Glen Doimhan, but 1,000 years ago it was more common and widespread in the vicinity of Loch a’Mhuilinn than it is today.

Value to wildlife

Arran whitebeam produces good pollen when growing in favourable conditions. The wild deer love the leaves (which is one of the reasons the tree population is struggling) and birds eat the ripe berries.

Did you know?

Seedlings are clones of the parent tree, producing asexually and thereby reducing genetic variation which makes them vulnerable to changes in the environment.

Threats and conservation

Arran whitebeam is on the International Union for Conservation of Nature (IUCN) Red List of endangered species because there are so few individual trees left and its range is very restricted. The population of only 407 individual trees are spread across an area covering just 20km2 in three locations.

Many of these are small, windswept and stunted and it is believed that over half of them are not reproducing and those that are cannot regenerate fast enough to recover from threats such as habitat loss, overgrazing, exposure to gales and heavy snow storms, and pests.