With all the doom and gloom of Chalara ash dieback and other tree pests and diseases, it was encouraging to read this week that scientists have made a step forward in attempts to save Scotland’s most endangered tree, the Catacol whitebeam.
Sorbus pseudomeincichii was first recorded in 2007, with only two specimens found on the Isle of Arran, one of which has since died. Attempts to grow the tree, from seed, or to graft it onto rowan rootstock, met with failure, but now a plant has finally been grown from a cutting. Eventually, enough cuttings may be grown on to keep the lonely Arran tree company.
The UK’s native whitebeams are a funny collection of species. They include all 12 British native tree species recorded as endangered in the World Conservation Monitoring Centre’s List of Threatened Trees. Vulnerable to grazing, they’re found mostly in steep, inaccessible places, and are often endemic to particular geographical areas.
The UK’s species of Sorbus includes three that are widespread and reproduce sexually – rowan, common whitebeam, and the wild service tree. However, there are also many species that are “apomictic” – they can set seed without fertilisation, and the offspring are effectively clones of their parents. Some of these have arisen originally through hybridisation with rowan.
Ley’s whitebeam for example, comprises a handful of trees found on only two sites in South Wales. Other rare species are found in the Brecon Beacons, Lancaster coast, and Devon and Somerset coasts. Ireland has its own endemic species, Sorbus hibernica.
With their attractive, white-backed leaves and clusters of red and orange fruit in the autumn, the endemic whitebeams are some of our most intriguing trees, demonstrating evolution in action. Because they do not have wide genetic variability, they may be even less resilient than many of our other native species – worrying in the face of climate change and tree disease. But then again, the common dandelion is also apomictic, and nothing seems to be slowing it down, so perhaps there is hope yet!
Sian Atkinson, Conservation Adviser