therefore occupies a less competitive niche with fewer tree species able to tolerate the harsher conditions. The rock whitebeam interbred with the rowan / mountain ash (Sorbus aucuparia) to produce the hybrid, a fertile separate species the Scottish whitebeam (Sorbus arranesis) which grows well in this zone of reduced competitive growth at higher altitudes. The bastard mountain ash (Sorbus pseudofennica) arose from a further cross between S. arranensis and the mountain ash (S. aucuparia). The Sorbus group are apomictic, producing viable seed without the need for pollination and fertilisation. Each time this hybrid cross occurs a new clone is effectively produced. Smart showed by using physical characteristics that the species were separate and not a result of random variation. Some overlap does however occur and this suggests that some hybridising may occur between the two species. A number of other Sorbus species have been produced in this way, such as the Devon whitebeam, the Bristol whitebeam, the Cheddar whitebeam, Irish whitebeam, Lancaster whitebeam, etc. All are rare and require careful protection and expert habitat management if they are to survive in the wild. In Scandinavia, particularly Norway, similar species have evolved following similar evolutionary pressures, but quite independently of the Arran whitebeams. Islands are well known as sites of endemic species. The Lundy cabbage (Coincya wrightii) is another British example, only growing on Lundy Island off the North Devon coast. Characteristics The mountain ash has a leaf made up of a number of leaflets, whilst the whitebeam leaf is entire and doesn't even have lobes. The result of crossing the two is that the hybrids begin to merge or mix characteristics, so that S. arranensis has lobes but no leaflets, while S. pseudofennica, having an extra cross with the "leafleted" mountain ash, has a variable number of true leaflets and lobes. These characteristics are not always definitive and sometimes the actual species cannot be ascertained with certainty, possibly due to hybridisation between the species in question. Some differences in the flower and seed characteristics are also noted. Unlike other endemic British species, they do not seem to grow on base-rich soils. Future prospects Although actual numbers haven't dropped since the first quantitative survey was carried out in 1897, this may be a false impression, since with more searching more have been found, which does not necessarily suggest a stable population. Various attempts at introducing saplings grown from native seed have