These trees, sometimes called Scottish sagebrush or Arran sagebrush (Sorbus arranensis), solid rowan or cut-leaf sagebrush (Sorbus pseudofennica), and catacols sagebrush (Sorbus pseudomeinichii), are among the most endangered tree species in the world if rarity is measured solely by numbers. They are protected at Glen Diormuhan off the coast of Glen Catacol, formerly part of the National Nature Reserve. Although this designation was removed in 2011, the area remains an Area of Special Scientific Interest (SSSI). In 1980, only 283 Aran lice and 236 cut leaf lice were recorded as mature trees, suggesting that grazing pressure and pest damage are preventing forest regeneration. It is typically a tree on the slopes of mountains close to the forest line. However, it also grows at lower elevations and is grown within Brodick Country Park. The North Ayrshire Council Parks and Recreation staff also cultivate specimens for conservation purposes. Several specialist horticultural centers and nurseries can supply them as grafts, and the Ardrossan Academy in North Ayrshire has prepared grafted specimens for use within a Scottish Higher Biology course, in which it is an example of evolution and survival of the fittest.
= Distribution =
Sorbus arranensis: Abhainn Beag (Uisge solus)、Glen Diomhan (式支流)、Glen Catacol、Allt nan Calman、Allt Dubh、Glen Easan Biorach、Glen Iorsa (Allt-nan-Champ). Sorbus pseudofennica: Abhainn Beag (Freshwater)、Glen Diomhan、Allt nan Calma。 ナナカマド pseudomeinichii: グレン カタコル。
The earliest preserved specimen is of Roxas tonelicus S. pseudofennica, collected from North Arran in 1797, with another 1838 dated specimen of the same species in the British Museum, then known as Pyrus pinnatifida (Pear Group). S. pseudofennica was authoritatively recognized as a separate species by Clapham, Tutin and Warburg in 1952. In 1875 Landsborough noted two species growing in Glen Diomhan and called them French rowan or white clover. The Scottish rowan, S. arranensis, aroused the most collecting interest in 1870-1890 and 1920-1940, but older specimens exist.
The trees developed in a very complex way, from the common louse (Sorbus aria) to the tetraploid rock louse (Sorbus rupicola), which is still found on Holy Island. Because the species can survive at high altitudes, it occupies a less competitive niche with fewer tree species able to withstand more extreme conditions. Rock lice have crossed with rowan/rowan (Sorbus aucuparia) to produce another highly fertile species, the Scottish louse (Sorbus arranesis). This hybrid grows well in this zone where growth at high altitudes is less competitive. Rowan (Sorbus pseudofennica) resulted from a further cross between S. arranensis and Rowan (S. aucuparia). The Sorbus group is apomic and produces viable seeds without the need for pollination or fertilization. Each time this hybrid crossing occurs, it effectively produces a new clone. Smart used physical features to show that the species were separate and not the result of random variation. However, some duplication did occur, suggesting that some interbreeding may occur between the two species. Many other rowan species are made this way, including Devon lice, Bristol lice, Cheddar lice, Irish lice and Lancaster lice. All are rare and require careful conservation and expert habitat management to survive in the wild. In Scandinavia, particularly Norway, similar species evolved under similar evolutionary pressures, but quite independently of Arancidium. The islands are well known for their endemic habitat. Lundy cabbage (Coincya wrightii) is also a British example, grown only on Lundy Island off the north Devon coast.
Rowan leaves are composed of numerous leaflets, while sage leaves are whole and do not even have lobes. As a result of crossing the two, hybrids began to fuse or mix features, with S. arranensis having lobules but no lobules, while S. pseudofennica has varying numbers of true lobules and lobules due to the extra crosses with the 'leaflet' Mountain Fraxinus. These characteristics are not always definitive and may not reliably identify the actual species, possibly due to hybridization between the species in question. There are also some differences in the characteristics of flowers and seeds. Unlike other British endemic species, it does not appear to grow in base-rich soils.
Although the actual numbers have not declined since the first quantitative survey was conducted in 1897, this may be a false impression as more searches are finding more and do not necessarily suggest a stable population. Various attempts to introduce seedlings grown from native species have met with varying degrees of success. Sheep grazing probably reduced the population from its widespread range to its present state, confining it to steep slopes and cracks in the rocks, and to the mountains at the northern tip of the island. The tree is not well known to islanders, and two fine specimens were even cut down in the 1980s by professional gardeners working on site near Brodick Castle. Rangers have taken steps to increase the tree's distribution and have planted both species in the park. But more could be done to make visitors and islanders aware of these unique species owned by Alan.
Catacol whitebeam - a new species
In 2007, it was announced that two specimens of the newly named catacols whitebeam (Sorbus pseudomeinichii) had been discovered by researchers on the Isle of Arran. The tree, also a native rowan-silabi hybrid, was discovered after research at the Scottish Natural Heritage (SNH), Dougary Estate, Edinburgh Royal Botanic Gardens. A study on the genetics of the locust tree showed that its population was much more diverse than previously thought, and that the louse seems to be gradually evolving towards a new type of tree, possibly very similar to rowan. A team at the Royal Botanic Gardens collected seeds and cuttings to ensure the long-term survival of the tree and took steps to protect the two known specimens. As of 2016, only one of two specimens has been found.
Rob Gibson, "The Battle to Save Alan Whitebeam", by Mandy Meikle (ed.), Reforesting Scotland 31, Spring 2004, pp. 35 & 36, ISSN 0969-1367
Aran lice in Eglinton Country Park Mainland.
 Alan Whitebeam of Ardrossan Academy
Definition & Meaning