Buckthorn Bark is often referred to as alder buckthorn; botanists know it by its scientific name, Rhamnus frangula. Although included in the category of bulk herbs for sale, buckthorn bark is really from the outer skin of a tree, or the bark - something that true herbs (which are perennials) lack.
In Europe, some cosmetics companies have recently taken to using an extract of cut Rhamnus frangula bark as an ingredient for sunblock.