Robinia pseudoacacia

The roots of black locust contain nodules that allow it to fix nitrogen, as is common within the pea family. Trees reach a typical height of with a diameter of . It is a very upright tree with a straight trunk and narrow crown that grows scraggly with age. The bark is a reddish black and gray and tinged with red or orange in the grooves; it is deeply furrowed into grooves and ridges which run up and down the trunk and often cross and form diamond shapes., and are compound, meaning that each leaf contains many smaller leaflike structures called leaflets, which are roughly paired on either side of the stem that runs through the leaf (rachis). There is typically one leaflet at the tip of the leaf (odd pinnate), and the leaves are alternately arranged on the stem. Each leaf is long and contains 9–19 leaflets, each being long and wide. The leaflets are rounded or slightly indented at the tip and typically rounded at the base. The leaves come out of the bud folded in half, yellow green, covered with silvery down which soon disappears. Each leaflet initially has a minute stipel, which quickly falls, and is connected to the (rachis) by a short stem or petiolule. The leaves are attached to the branch with slender hairy petioles which are grooved and swollen at the base. The stipules are linear, downy, membranous at first and occasionally develop into prickles. The leaves appear relatively late in spring, and turn a clear pale yellow in autumn. The leaflets fold together in wet weather and at night (nyctinasty), as some change of position at night is a habit of the entire leguminous family. Young trees are often spiny, especially on root suckers and branches near the ground; mature trees often lack spines. R. pseudoacacia is quite variable in the number of spines present, as some trees are densely prickly and other trees have no prickles at all. The spines typically remain on the tree until the young thin bark to which they are attached is replaced by the thicker mature bark. They develop from stipules (small leaf-like structures that grow at the base of leaves), and since stipules are paired at the base of leaves, the spines will be paired at the bases of leaves. They are up to long and somewhat triangular with a flared base and sharp point. Their color is a dark purple and they adhere only to the bark. There are typically 25,500 seeds per pound. Cotyledons are oval in shape and fleshy. Reproduction and dispersal Black locust reproduces both sexually via flowers, and asexually via root suckers. The flowers are pollinated by insects, primarily by Hymenopteran insects. The physical construction of the flower separates the male and female parts so that self-pollination will not typically occur. The seedlings grow rapidly but they have a thick seed coat which means that not all seeds will germinate. The seed coat can be weakened via hot water, sulfuric acid, or be mechanically scarified, which will allow a greater quantity of the seeds to grow. Black locust has been found to have either 2n=20 or 2n=22 chromosomes. Flavonoid content Black locust leaves contain flavone glycosides characterised by spectroscopic and chemical methods as the 7-O-β-ᴅ-glucuronopyranosyl-(1→2)[α-ʟ-rhamnopyranosyl-(1→6)]-β-ᴅ-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). Similar species Although similar in general appearance to the honey locust, the black locust lacks that tree's characteristic long branched thorns on the trunk, having instead pairs of short prickles at the base of each leaf; the leaflets are also much broader than honey locust. It may resemble Styphnolobium japonicum, which has smaller flower spikes and lacks spines. == Taxonomy ==

The black locust is a plant from the subfamily of Faboideae in the family of legumes (Fabaceae) and is a relative of the pea and bean. The black locust is commonly referred to as "false acacia" after its species name "pseudoacacia", although it is not particularly closely related to the acacia, which belongs to the mimosa subfamily (Mimosoideae). Both species are similar in the form of their feathered leaves and thorns, but the flower shapes are very different. Confusion between species of both genera is almost impossible in higher latitudes, since acacias are native to subtropical and tropical areas and do not thrive in the cooler climates favoured by the black locust. == History ==

The tree was identified in 1607 at Jamestown by British colonists, who used the timber to build houses. The tree was named for its resemblance to Ceratonia siliqua, known as the "Old World Locust". Introduction in Europe The genus is named after the royal French gardeners Jean Robin and his son . Today, The Jardin des Plantes botanical garden in Paris, France, says Jean Robin planted a black locust tree in France in his own garden located in ''L'île de la Cité, Paris, circa 1600 (previously said to be in 1601 or 1602), his son Vespasien later uprooting and transplanting the very same tree circa 1630 in the actual Jardin des Plantes'' botanical garden in Paris (previously thought to originate from an offshoot of the tree planted by the father, while the now revised official story states the original tree being uprooted had offshoots grow later from some of the roots which were still left in the soil in its initial location). Jean Robin is said to have obtained the seeds which served to plant the tree in question from his friend John Tradescant the Elder, an English naturalist. It was introduced into Britain in 1636. According to research by Hungarian naturalist József Ernyey, the proliferation of the Black Locust in the mid-18th century was closely linked to the Seven Years' War (1756–1763). Recognizing the tree's rapid growth and dense habit, the military administration of the Habsburg Monarchy utilized the species as a defensive tool. Under orders from Queen Maria Theresa, Robinia pseudoacacia was planted near fortifications to create physical obstacles that hindered the movement of enemy infantry and the positioning of artillery. The species saw a second major wave of planting following World War I. In the wake of territorial losses and environmental concerns regarding the increasing aridity of the Great Hungarian Plain, the Hungarian government launched large-scale afforestation programs. The Black Locust was favored for its ability to stabilize sandy soil and reverse erosion, leading the state to override private property rights to enforce its planting. == Distribution ==

The genus Robinia is native to North America, although traces of it are found in Eocene and Miocene rocks in Europe. as it has been cultivated and is now found in all 48 lower states, British Columbia, and eastern Canada. Eurasia, and Africa. Humans have distributed the tree for landscaping, with its range now including Canada, Southern South America, Europe, temperate regions in Asia (including China, India, and Pakistan), Northern and Southern Africa, Australia, and New Zealand. == Ecology ==

Black locust is a shade-intolerant species and provides valuable cover when planted on previously open areas. Its seeds are eaten by bobwhite quail and other game birds and squirrels. Woodpeckers may nest in the trunk since older trees are often infected by heart rot. The deeply grooved bark also makes it a preferred species for some bat roosts. Herbivores Locust leaf miner Odontota dorsalis attacks the tree in spring and turns the leaves brown by mid summer, slowing the growth of the tree though not seriously. Other insect species feeding on black locust in its native range are the gall midge Obolodiplosis robiniae, the sawflies Euura tibialis and Nematus abbotii, and a number of Lepidoptera: Agonopterix robiniella (Depressariidae), Filatima pseudacaciella (Gelechiidae), Ecdytolopha insiticiana (Tortricidae), Euparthenos nubilis and Zale unilineata in Erebidae, Sciota subcaesiella (Pyralidae), and the Gracillariidae leafminers Chrysaster ostensackenella, Macrosaccus robiniella and Parectopa robiniella. Black locust is also attacked by Chlorogenus robiniae, a virus which causes witch's broom growths; clear leaflet veins are a symptom of the disease. Invasiveness Black locust is considered invasive on its native continent, specifically in the western United States, New England region, northern California, and in the Midwest. In the prairie and savanna regions of the Midwest, black locust can dominate and shade open habitats. These ecosystems have been decreasing in size, and black locust is contributing to this reduction; when black locust invades an area, it will convert the grassland ecosystem into a forested ecosystem where the grasses are displaced. Black locust has been listed as invasive in Connecticut, Wisconsin, and Michigan, and is prohibited in Massachusetts. In Australia, black locust has become naturalized within Victoria, New South Wales, South Australia and Western Australia. It is considered an environmental weed there. Black locust outcompetes nearby trees with its extreme growth rate, remaining herbaceous longer than most woody species. In Kashmir, India, the average height growth rate of black locust was per year. Hungary Today, the tree is economically significant in Hungary as a source of high-energy firewood and for the production of acacia honey. However, it is also ecologically disruptive, as it outcompetes endogenous tree species and converts open grassland habitats into shrublands, threatening rare native flora. In 2014, a political conflict arose when the European Union considered classifying Robinia pseudoacacia as an invasive species. The Hungarian government opposed this classification, declaring the tree a "Hungaricum"—a protected element of national cultural heritage—effectively politicizing the species' biological status. == Toxicity ==

The bark, leaves, and wood are toxic to both humans and livestock. Important constituents of the plant are the toxalbumin robin, which loses its toxicity when heated, and robinin, a nontoxic glucoside. 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 sawdust and shavings from Robinia lumber can cause contact dermatitis in sensitive persons. == Cultivation and uses ==

, Armenia Black locust can be easily propagated from roots, softwood, or hardwood. Cultivars Several cultivars exist, 'Frisia' being one of the most planted ones. • 'Decaisneana' has been considered a cultivar but is more accurately a hybrid (R. pseudoacacia x R. viscosa). It has light rose-pink colored flowers and small or no prickles. • 'Frisia', a selection with bright yellow-green leaves and red prickles, is occasionally planted as an ornamental tree. • 'Unifoliola', a plant with fewer leaflets, no prickles, and a shorter height. Black locust has been spread and used as a plant for erosion control as it is fast growing and generally a tough tree. Other produce In traditional medicine of India, different parts of R. pseudoacacia are used as laxative, antispasmodic, and diuretic. In Liguria, Italy and Romania the flowers are sometimes used to produce a sweet and perfumed jam. This means manual harvesting of flowers, eliminating the seeds and boiling the petals with sugar, in certain proportions, to obtain a light sweet and delicate perfume jam. Although the bark and leaves are toxic, various reports suggest that the seeds and the young pods of the black locust are edible. Shelled seeds are safe to harvest from summer through fall, and are edible both raw and boiled. Due to the small size of the seeds, shelling them efficiently can prove tedious and difficult. In France, Italy and Romania, R. pseudoacacia flowers are eaten as beignets after being coated in batter and fried in oil; they are also eaten in Japan, largely as tempura. Erosion control The species is considered excellent for growing in disturbed areas as an erosion control plant. 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. For best results, it should be seasoned like any other hardwood, but black locust is also popular because of its ability to burn even when wet. 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. If the black locust is cut, split, and cured while relatively young (within 10 years), thus minimizing beetle damage, "spitting" problems are minimal. Construction This native hardwood is also prized by North American shipwrights for making rot-resistant trunnels in traditional wooden ship construction. The wood is extremely hard, being one of the hardest woods in Northern America with a Janka hardness test of 1,700 lbf (7,560 N) and specific gravity of 0.733 (733 kilograms per cubic metre or 45.7 pounds per cubic foot). It is very resistant to rot, and durable, making it prized for furniture, flooring, paneling, fence posts, and small watercraft. Wet, newly cut planks have an offensive odor which disappears with seasoning. Black locust is still in use in some rustic handrail systems. In the Netherlands and some other parts of Europe, black locust is one of the most rot-resistant local trees, and projects have started to limit the use of tropical wood by promoting this tree and creating plantations. Flavonoids in the heartwood allow the wood to last over 100 years in soil. With a light yellowish color and strength, the wood was much used for decorative inlays and banding in furniture in England and France in the 17th and 18th centuries, under the name "acacia" or "Virginia acacia". Recently, Robinia has become popular for outdoor furniture and playground equipment. In 1900, the value of Robinia pseudoacacia was reported to be practically destroyed in nearly all parts of the U.S. 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. == In culture ==

In Asia, many black locusts, called cihuai (:zh:刺槐), yanghuai (foreign huai :zh:洋槐, against native huai :zh:国槐) or simply "acacias", were planted in Dalian, Liaoning, China, during its Russian and Japanese occupation, and are loved by the local people: there is Acacia Avenue (槐树大道) in downtown; the Acacia Flower Festival (槐花節) is celebrated every year in May; and acacia honey is collected in the suburbs by bee keepers. The Locust of Square René-Viviani is the oldest tree in Paris. == References ==