Whitebeams (Sorbus spp)
The genus of Sorbus trees comprises a widely differing group. The family includes rowan, also known as the mountain ash Sorbus aucuparia, wild service tree S. torminalis, service tree S. domestica, and whitebeam S. aria. Their sizes range from 5 m for some of the isolated and exposed varieties, up to 25 m in the case of the wild service tree. Their leaves also display a wide variety of shapes, some resembling the ash and others with a similar appearance to maple or hornbeam.
Whitebeam is notorious for producing local varieties, some of these restricted to a handful of individuals confined to an extremely small area. There are believed to be about 14 separate species, but it is possible that new varieties will continue to be discovered - or even evolve - on inaccessible cliffs the British Isles.
Rowan is found all over Britain, chiefly on acid or light soils. Wild service tree is confined, largely, to southern England and seems to be an indicator of ancient woodland and hedgerow. Its stronghold is in the area of Kent, Sussex and Hampshire known as the Weald, and here there seems to be a curious connection. The berries of the tree are known locally as 'chequers' from their speckled markings, and were popular as food. These berries may have been the source of the name of 'Chequers Inn', many examples of which exist in this South-East corner of England.
The discovery of the range of the service tree is an intriguing and complicated story. It is now believed that the tree was once fairly common over Wales, the South-West and the Midlands but, until quite recently, the only 'wild' specimen was thought to exist in the Wyre Forest. Then a relic population of wild trees was discovered on cliffs in South Glamorgan. From their location it is certain they were not 'planted' by humans as has happened in collections and arboreta elsewhere in England. Some botanists have suggested that other cliff-faces in the south of England should be examined to see if more undiscovered populations exist.
Whitebeam, in its various local forms, is found in isolated places throughout England, Scotland and Wales. One of these species, S. leyana, is limited in its range to a few shrubs growing near Merthyr Tydfil in Brecon whilst, S. wilmottiana is found only in the Avon Gorge near Bristol.
The four main species, aria, aucuparia, torminalis and domestica are found throughout central and southern Europe.
The requirements of these different species vary from acid soil to crumbling limestone rock.
Rowan gets its alternative name of mountain ash from its abundance in upland areas and from the shape and pattern of its leaves, which resemble its unrelated namesake. It produces a large crop of vivid orange berries, popular with humans as well as birds. There is a long history of superstition connected with this tree and it his believed to have certain magical powers. In Scotland, for instance, it is considered unlucky to cut down a rowan.
Wild service tree, service tree and whitebeam also produce fruit, but they rarely ripen in the British climate and it is thought that these trees spread mainly from shoots or suckers. The fruit has been eaten in many parts of the country but it has to be left to go rotten, or 'bletted' before they are edible. Wild service tree's 'chequers' and whitebeam fruit have also been used for making alcoholic liquor, no doubt sold in the many Chequers Inns.
Rowan is a common species, more particularly as it has been planted as an amenity tree in gardens and along residential streets in towns and cities, as have whitebeams.
The other species, it seems, have never been particularly common in the UK, particularly the 14 'micro' species. It is quite possible that they are on the northern edge of their range, especially in the case of the whitebeam. It is difficult to assess whether they are truly endangered in the accepted sense, as it is by no mean certain that they were ever common in this county. Sorbus domestica is rare and may have declined considerably in recent years.
The various rare whitebeam species are included in English Nature's Species Recovery Programme whilst S. leyana is listed in the UK Biodiversity Action Plans. Work on these species is limited, primarily, to protecting the sites where they occur and carrying out genetic studies to ascertain their provenance. It is highly likely that other curious and isolated varieties of Sorbus may be discovered in isolated, and almost inaccessible parts of the British Isles.
Information supplied by English Nature.