Uses
The Purging Buckthorn or Common Buckthorn (R. cathartica) is a widespread European native species, in the past used as a purgative, though its toxicity makes this a very risky herbal medicine and it is no longer used. Introduced into the United States as a garden shrub, this has become an invasive species in many areas there. It has recently been discovered to be a primary host of the soybean aphid (Aphis glycines), a problem pest for soybean farmers across the US. The aphids use the buckthorn as a host for the winter and then spread to nearby soybean fields in the spring.
Another European species, Alder Buckthorn (R. frangula, syn. Frangula alnus) was of major military importance in the 15th to 19th centuries, as its wood provided the best quality charcoal for gunpowder manufacture.
Italian Buckthorn (R. alaternus), an evergreen species from the Mediterranean region, has become a serious weed in some parts of New Zealand—especially on Hauraki Gulf islands.
Dyer's Buckthorn (R. tinctoria) is used, together with the Asian Chinese Buckthorn (R. utilis), to produce the dye "china green". Another species, Avignon Buckthorn (R. saxatilis) provides the yellow dye Persian berry, made from the berries.
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