Alien plants are now a significant component of the British flora. Whilst a few alien species such as Japanese Knotweed Fallopia japonica, New Zealand Pigmyweed Crassula helmsii, and Himalayan Balsam Impatiens glandulifera have become highly invasive most are not a direct threat to our native species. Many aliens have failed to establish widely and populations of some of these species are often regarded as ‘honorary rarities’. A great example of this is Purple Coltsfoot Homogyne alpina that is restricted to a single rock ledge in Glen Clova. It was ‘discovered’ by the great alpine plant hunter George Don in 1813. There has been much debate on its status as a native plant but it is generally considered to have been introduced, probably by George Don himself. Sadly, and despite the efforts of Scottish Natural Heritage, the Purple Coltsfoot has declined rapidly in recent times; it once covered a quite sizable area but it is now close to extinction. Other rare aliens that we hold in cultivation include Tower Cress Arabis turrita, Asarabacca Asarum europaeum, Somerset Skullcap Scutellaria altissima, Worcester Catchfly Silene catholica, Dragon’s Teeth Tetragonolobus maritimus, and Mediterranean Nettle Urtica membranacea.