Royal Botanic Garden Edinburgh (RBGE) is leading a project to save some of the most endangered trees in the country.
One of the species, Catacol whitebeam, is named after Glen Catacol in the north of Arran where it was discovered.
Today, it is represented in the wild by a single known tree and thus qualifies for Critically Endangered.
It is the third offspring of this family and arose from a natural crossing between the second offspring, Arran service-tree and one of its parents, rowan.
The rare species have been planted in the grounds of Great Glen House, the headquarters of Scottish Natural Heritage (SNH) in the Highland capital.
A plaque illustrating how the three species evolved was unveiled by Susan Davies, chief executive for Scottish Natural Heritage (SNH).
Ms Davies said, “There are very few species which truly belong to Scotland and to nowhere else in the world.
“The Arran whitebeams are one such species. It would be special to have just one tree species originate from a Scottish island, but for three to arise in a tiny area of one island is amazing.”
Simon Milne, RBGE Regius Keeper, said, “It is very exciting to have endemic species evolving here in Scotland and the sorbus trees on Arran are fascinating.
“The evolution of these trees makes Arran a natural laboratory for studying species diversification. What we need to do now is to ensure their long term conservation and retain opportunities for further evolution.”
Genetic research carried out at Edinburgh University has shown that Arran whitebeam was the first new species and arose from crossing between the closely related rowan and rock whitebeam.
A similar cross is thought to have arisen independently in Scandinavia. Arran whitebeam then crossed with rowan to create the Arran service-tree which then crossed with rowan again to create Catacol whitebeam.
RGBE has also planted examples of the Arran whitebeams outside the Scottish Parliament and on the island of Arran for public display.
An example of each of the three endemic species, and the two species which gave rise to them, can be viewed in the grounds of Great Glen House, Leachkin Road, Inverness.
The grounds are open to the public to visit and include a variety of habitats comprising native plant species.
Great Glen House is the shared Scottish headquarters for SNH, the Crofting Commission and Bòrd na Gàidhlig. The office also houses the Crown Office & Procurator Fiscal Service for Inverness.