Black locust

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iBlack Locust

Flowers

Scientific classification

Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Fabales
Family:	Fabaceae
Subfamily:	Faboideae
Tribe:	Robinieae
Genus:	Robinia
Species:	R. pseudoacacia

Binomial name

Robinia pseudoacacia
L.

Black Locust (Robinia pseudoacacia) 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 and Asia and is considered an invasive species in some areas.

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 intensely fragrant flowers are white, borne in pendulous racemes 8–20 cm long, and are considered edible. 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 but they are smaller, lighter, and easily carried long distances by the wind. Unlike honey locust, but like the related European Laburnum, the pods are toxic. In fact, every part of the tree except the flowers is considered toxic.

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.

[edit] 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 the cultivar 'Frisia', a selection with bright yellow-green leaves, is occasionally planted as an ornamental tree.

The wood is extremely hard, 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. 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.