their naturally aggressive propagation. One of the most globally significant invasive acacias is black wattle A. mearnsii, which is taking over grasslands and abandoned agricultural areas worldwide, especially in moderate coastal and island regions where mild climate promotes its spread. Australian/New Zealand Weed Risk Assessment gives it a "high risk, score of 15" rating and it is considered one of the world's 100 most invasive species. Extensive ecological studies should be performed before further introduction of acacia varieties, as this fast-growing genus, once introduced, spreads quickly and is extremely difficult to eradicate. Phytochemistry Cyanogenic glycosides Nineteen different species of Acacia in the Americas contain cyanogenic glycosides, which, if exposed to an enzyme which specifically splits glycosides, can release hydrogen cyanide (HCN) in the "leaves". This sometimes results in the poisoning death of livestock. If fresh plant material spontaneously produces 200 ppm or more HCN, then it is potentially toxic. This corresponds to about 7.5 μmol HCN per gram of fresh plant material. It turns out that, if acacia "leaves" lack the specific glycoside-splitting enzyme, then they may be less toxic than otherwise, even those containing significant quantities of cyanic glycosides. Some Acacia species containing cyanogens include Acacia erioloba, A. cunninghamii, A. obtusifolia, A. sieberiana, and A. sieberiana var. woodii Famous acacias The Arbre du Ténéré in Niger was the most isolated tree in the world, about from any other tree. The tree was knocked down by a truck driver in 1973. In Nairobi, Kenya, the Thorn Tree Café is named after a Naivasha thorn tree (Acacia xanthophloea) in its centre. Travelers used to pin notes to others to the thorns of the tree. The current tree is the third of the same variety. References Further reading Shulgin, Alexander and Ann, TiHKAL the Continuation. Transform Press, 1997. External links World Wide Wattle Acacia-world Wayne's Word on "The Unforgettable Acacias" The genus Acacia and Entheogenic Tryptamines, with reference to Australian and related species, by mulga A description of Acacia from Pomet's 1709 reference book, History of Druggs Dr. Duke's Phytochemical and Ethnobotanical Databases Flora identification tools from the State Herbarium of South Australia Tannins in Some Interrelated Wattles List of Acacia Species in the U.S. FAO Timber Properties of Various Acacia Species FAO Comparison of Various Acacia Species as Forage Vet. Path. ResultsAFIP Wednesday Slide Conference – No. 21 February 24, 1999 Acacia cyanophylla lindl as supplementary feed/for small stock in Libya