what is the purging buckthorn
About. Purging Buckthorn, sometimes simply known as just 'Buckthorn', is a small, spiny tree of woodland, scrub and hedgerows on chalky soils. It is widespread, but scarce, across the lowland areas of central and eastern England.lusters of small yellow-green flowers appear in late spring and bunches of poisonous black berries ripen in autumn. Purging Buckthorn is the main foodplant of the Brimstone Butterfly in the areas where it grows, but Alder Buckthorn is used as an alternative.