The Catacol Whitebeam (Sorbus pseudomeinichii) is a rare tree endemic to the Isle of Arran in south west Scotland. It is believed to have arisen as a hybrid of the native Rowan (Sorbus aucuparia) and the Cut-leaved Whitebeam (Sorbus pseudofennica) which is in turn a Rowan/Arran Whitebeam (Sorbus arranensis) hybrid. Only two specimens of the Catacol Whitebeam are known, making it the rarest tree in Scotland and also the United Kingdom. A third was recorded as a sapling but is believed to have been destroyed by deer. A seedling has also been grown in Edinburgh.
The discovery followed work in the 1990s by Scottish Natural Heritage (SNH), Dougarie Estate and Royal Botanic Garden Edinburgh. The trees were confirmed as a distinct species by DNA testing.
Graeme Walker of SNH has said:
"These are unique trees which are native to Arran and not found anywhere else in the world, we knew about the Arran Whitebeam and the Cut-leaved Arran Whitebeam, which are also crosses between rowan and different species of whitebeam, but it has been really exciting to discover a completely new species. It is very complex picture but we think that the Arran Whitebeams are gradually evolving towards a new type of tree which will probably look very similar to a rowan."
Dr. Ashley Robertson of Bristol University, who helped discover the species, said: "It is not an evolutionary dead end. It is evolution in action".
The new species is the third endemic whitebeam found on Arran (after the Arran Whitebeam and the Cut-leaved Whitebeam) and combines the red berries of a rowan with the oval leaves of a whitebeam. The trees are currently within a deer fence which will be extended - delivery of materials by helicopter will be necessary due to the remoteness of the location. The species is named after Glen Catacol where it was found and one of the two surviving plants is thought to be more than fifty years old.