Alder Buckthorn (Rhamanus Frangula) is a small, thornless tree of wet woodland, riverbanks and heath lands. It is widespread, but scarce across England and Wales. Clusters of pale green flowers appear in late spring and bunches of red berries ripen to a purple-black colour in autumn. Both Alder and Purging buckthorn are the main food plants of the Brimstone Butterfly. It's a British native ideal for damp peaty soils. It provides good cover and food for game birds. Alder Buckthorn is totally wind firm and completely hardy. More Buckthorn trees here