Black locust, Robinia pseudoacacia, is a tough, medium-sized member of the legume family. Originally native to the southern Appalachians and Ozarks, it's now spontaneous over a much wider range, extending into southern Canada and west to Missouri and Oklahoma. 

In much of Europe, many parts of Asia, and some of South America, it holds its own against native vegetation. Also known as false-acacia or rose-acacia, this species grows up to 100 feet high. Its deeply furrowed trunk grows up to 4 feet wide.  Locust shoots are characteristically armed with paired spines, although a spineless variety exists.  Beautiful lacy green leaves appear in late spring. Long, fragrant racemes of creamy white flowers blossom in May or June.  In fall, the leaves change to yellow before they drop. The fruits are flattened pea-like pods.

This handsome species does have some potential negative attributes:

• A fast-growing tree with a shallow, aggressive root system, it can be highly invasive.
• As a legume, black locust fixes nitrogen. In low-nutrient habitats, this nitrogen fixing facilitates invasion by weedy, nitrogen-loving non-natives.
• Black locust contains several toxic components in its leaves, stems, bark and seeds. Ingestion results in gastrointestinal and neurological effects--particularly acute in horses--which may be fatal.

Its name honors Jean and Vespasien Robin, father and son, 16th- and 17th-century herbalists to the king of France. The father obtained seeds from America in 1601 introduced Robinia to Europe, raising plants in a botanic garden he established in Paris. One of his specimens still stands in Paris's Jardin des Plantes, where it is known as the oldest tree in Paris.

The common name locust reflects the confusion of early American settlers, who identified the tree with the carob (Ceratonia), the fruits of which were thought to be the locusts that John the Baptist ate in the wilderness.

Black locust wood is extremely durable when exposed to moisture and so is highly valued for fences, as well as pergolas and other garden uses. Authentic records exist of fenceposts remaining in good condition after standing in the ground for 125 years. The wood also has the virtue of not shrinking or swelling much; it was used for tree nails in wooden ships and for other construction. Black locust wood is reported to be 1 1/2 times as hard, tough, and strong as white oak (Quercus alba). It is an excellent, long-burning fuel.

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- Courtesy of NYBG Plant Information Service