Black locust
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Black Locust (Robinia pseudoacacia) is a tree in the subfamily Faboideae of the pea family Fabaceae. It is native to eastern North America from northeast Texas to New York, and widely planted and naturalised elsewhere in the rest of temperate North America, Europe and Asia.
It grows to 15-25 m tall, with a trunk up to 0.8 m diameter (exceptionally up to 27 m tall and 1.6 m diameter in very old trees), with thick, deeply furrowed blackish bark. The leaves are 10-25 cm long, pinnate with 9-19 oval leaflets, 2-5 cm long and 1.5-3 cm broad. Each leaf usually has a pair of short thorns at the base, 1-2 mm long or absent on adult crown shoots, up to 2 cm long on vigorous young plants. The flowers are white, in pendulous racemes 8-20 cm long. The fruit is a legume 5-10 cm long, containing 4-10 seeds.
Although similar in general appearance to Honey locust, it lacks that tree's characteristic long branched spines on the trunk, instead having the pairs of short thorns at the base of each leaf; the leaflets are also much broader.
As with honey locust, black locust reproduces through distinct hanging pods. However, unlike honey locust, but like the related European Laburnum, its pods are toxic. In fact, every part of the tree is considered toxic.
Black locust is a legume in the family Fabaceae, which makes it capable of hosting nitrogen-fixing bacteria on its root system.
Cultivation and uses
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.
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 there are cultivars that make good garden plants.
It is extremely hard wooded, resistant to rot and long lasting, making it prized for fence posts and small watercraft. As a young man, Abraham Lincoln spent a lot of time splitting rails and fence posts from black locust logs.
