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030  Robinia pseudoacacia L.


Nome comune: Robinia; Acacia; Gaggia

Robinia pseudoacacia, commonly known as the Black Locust, is a tree in the subfamily Faboideae of the pea family Fabaceae. It is native to the southeastern United States, but has been widely planted and naturalized elsewhere in temperate North America, Europe, Southern Africa [1] and Asia and is considered an invasive species in some areas. A less frequently used common name is False Acacia, which is a literal translation of the specific epithet. It was introduced into Britain in 1636. Black locust is a major honey plant in eastern USA, and, having been taken and planted in France, is the source of the renowned acacia monofloral honey from France. Flowering starts after 140 growing degree days. However, its blooming period is short (about 10 days) and it does not consistently produce a honey crop year after year. Weather conditions can have quite an effect on the amount of nectar collected as well; in Ohio state for example, good honey locust flow happens in one out of five years[4]. In Europe it is often planted alongside streets and in parks, especially in large cities, because it tolerates pollution well. The species is unsuitable for small gardens due to its large size and rapid growth, but the cultivar 'Frisia', a selection with bright yellow-green leaves, is occasionally planted as an ornamental tree. Black locust has nitrogen-fixing bacteria on its root system; for this reason it can grow on poor soils and is an early colonizer of disturbed areas. In 1900 it was reported that the value of Robinia pseudacacia is practically destroyed in nearly all parts of the United States beyond the mountain forests which are its home by locust borers which riddle the trunk and branches. Were it not for these insects, it would be one of the most valuable timber trees that could be planted in the northern and middle states. Young trees grow quickly and vigorously for a number of years, but soon become stunted and diseased, and rarely live long enough to attain any commercial value.[3] Black locust leaves contain flavone glycosides characterised by spectroscopic and chemical methods as the 7-O--d-glucuronopyranosyl-(1 ? 2)[a-l-rhamnopyranosyl-(1 ? 6)]--d-glucopyranosides of acacetin (5,7-dihydroxy-4'-methoxyflavone), apigenin (5,7,4'-trihydroxyflavone), diosmetin (5,7,3'-trihydroxy-4'-methoxyflavone) and luteolin (5,7,3',4'-tetrahydroxyflavone)[5]. The wood is extremely hard, resistant to rot and durable, making it prized for fence posts and small watercraft. As a young man, Abraham Lincoln spent much of his time splitting rails and fence posts from black locust logs. Flavonoids in the heartwood allow the wood to last over 100 years in soil.[6] In the Netherlands and some other parts of Europe, black locust is the most rot-resistant local tree, and projects have started to limit the use of tropical wood by promoting this tree and creating plantations. It is one of the heaviest and hardest woods in North America. Black Locust is highly valued as firewood for wood-burning stoves; it burns slowly, with little visible flame or smoke, and has a higher heat content than any other species that grows widely in the Eastern United States, comparable to the heat content of anthracite".[7] It is most easily ignited by insertion into a hot stove with an established coal bed.[citation needed] For best results it should be seasoned like any other hardwood, however black locust is also popular because of its ability to burn even when wet.[8] In fireplaces it can be less satisfactory because knots and beetle damage make the wood prone to "spitting" coals for distances of up to several feet.[citation needed] If the Black Locust is cut, split, and cured while relatively young (within ten years), thus minimizing beetle damage, "spitting" problems are minimal. It is also planted for firewood because it grows rapidly, is highly resilient in a variety of soils, and it grows back even faster from its stump after harvest by using the existing root system.[9] With fertilizer prices rising, the importance of black locust as a nitrogen-fixing species is also noteworthy. The mass application of fertilizers in agriculture and forestry is increasingly expensive; therefore nitrogen-fixing tree and shrub species are gaining importance in managed forestry.[8] Black locust's pods are small and light, and easily carried long distances. Although the bark and leaves are toxic, various reports suggest that the seeds and the young pods of the black locust can be edible when cooked, since the poisons that are contained in this plant are decomposed by heat. Important constituents of the plant are the toxalbumin robin, which loses its toxicity when heated and robinin, a non-toxic glucoside,[10] Horses that consume the plant show signs of anorexia, depression, incontinence, colic, weakness, and cardiac arrhythmia. Symptoms usually occur about 1 hour following consumption, and immediate veterinary attention is required. The name locust is said to have been given to Robinia by Jesuit missionaries, who fancied that this was the tree that supported St. John in the wilderness, but it is native only to North America. The locust tree of Spain (Ceratonia siliqua or Carob Tree), which is also native to Syria, is supposed to be the true locust of the New Testament; the fruit of this tree may be found in the shops under the name of St. John's bread.[3] Robinia is now a North American genus, but traces of it are found in the Eocene and Miocene rocks of Europe.[3]