A TREE that only grows on Arran has been identified as a new species by scientists.
The Catacol whitebeam, named after the glen in which it was found, is believed to be the rarest tree species in the UK, with just two known mature examples.
Three trees were discovered in the 1990s but DNA tests had to be done before the species could be formally recognised and given a Latin name, Sorbus pseudomeinichii.
Since then one tree has died. Of the others, one is thought to be close to death while one is healthy.
A seed has grown to a sapling at the Royal Botanic Garden Edinburgh and cuttings have also been taken in order to preserve the species.
The new species is a product of several generations of interbreeding between rowan trees and different types of whitebeam.
The Catacol whitebeam is a cross between a rowan and a cut-leaved whitebeam, itself a cross between a rowan and an Arran whitebeam, which was a hybrid of a rowan and a rock whitebeam.
Graeme Walker, an area officer for Scottish Natural Heritage, said the evolution of the whitebeams could be tracked through its genes.
"We have this fantastic example of the evolutionary process documented with all the different stages, which is absolutely fascinating," he said.
"It is a clear example of how the species can change and how it happens in a natural environment.
"There's a dilution of the rock whitebeam all the way through this. It's becoming more and more physically like the rowan. Eventually its appearance will be very similar to the rowan, but genetically it will be very different."
Dr Ashley Robertson, of Bristol University, who helped discover the species, said the tree was a species in its own right as it was able to reproduce.
"It is not an evolutionary dead end. It is evolution in action," he said.
However Dr Roberston said the new species' future was in the balance.
"There were three but one has gone already. There was a young one like a sapling but that probably got eaten by a deer. Another was quite an old one and there was only one branch left that was growing. The other one that's left is a healthy looking tree.
"But they are quite hardy and very attractive. I've been trying to grow some. I'd love to have one in my garden."