Also other animals prefer to leave buckthorns alone because their leaves are not appetizing and their fruits are toxic to some animals. Overall they are known to have a negative effect on their surrounding environment. For example, the European buckthorn is blamed for increased frog egg mortality from a chemical it releases. Other species, such as the Rhamnus alaternus also make chemicals that prevent other animals from consuming them. Ecology Some species are invasive outside their natural ranges. R. cathartica was introduced into the United States as a garden shrub and has become an invasive species in many areas there. It is a primary host of the soybean aphid (Aphis glycines), a 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. 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. Buckthorns are used as food plants by the larvae of many Lepidoptera species. The American species are known to be hosts for the oat fungus Puccinia coronata. In a 1930 study, both kerosene and salt were employed for eradication of R. lanceolata and both proved to be less expensive than felling these bushes. Uses The fruit of most species contain a yellow dye and the seeds are rich in protein. Oils from the seeds are used for making lubricating oil, printing ink, and soap. Many species have been used to make dyes. R. utilis provides china green, a dye used to give a bright green color to silk and wool. Another species, Avignon buckthorn (R. saxatilis) provides the yellow dye Persian berry, made from the fruit. Some species may cause demyelinating polyneuropathies. The purging buckthorn (R. cathartica) is a widespread European native species used in the past as a purgative. It was in mid 17th-century England the only native purgative. It was also known pre-Linnaeus as Spina Cervina. The berries of Spina Cervina are black and contain a greenish juice, along with four seeds apiece; this serves to distinguish them from those of the black alder and dogberry, which contain only one or two apiece. Its syrup is said to be churlish. Its toxicity makes this a very risky herbal medicine, and it is no longer in use. R. prinoides is known as