The North American Common Black Locust

Robinia pseudoacacia is Beautiful in the Landscape

Black Locust
Black Locust. Photo by Kim Nix

Robinia pseudoacacia, commonly known as the black locust, is a prickly tree within the subfamily Faboideae of the pea family called Fabaceae and is considered to be a legume with flattened pea pods several inches long. Black locust is native to the southeastern United States, but has been widely planted and naturalized elsewhere in temperate North America, Europe and Asia.

The original range of the locust is in the Appalachian, Ozark and Ouachita range located in the middle mountains of Eastern North America. They are now considered an invasive species in some areas even within the natural range. Black locust was introduced into Britain in 1636 where it has slowly garnered a universal appeal to tree lovers.

Black Locust Identification

One major identifier is the long compound leaves with up to 19 leaflets which present the typical and unique locust leaf profile (not to be confused with the twice compound leaves of honey locust). The other ID marker is a small stout briar spine on branches, often curved and in pairs at each leaf node.

Late spring to early summer flowers can be showy, white and drooping with 5-inch flower clusters. These flowers are fragrant with a vanilla and honey scent. The leguminous fruit developing from the flower has 4-inch papery thin pods with small, dark-brown, kidney-shaped seeds. These autumn seeds will persist until the next spring.

You will find this tree primarily in areas where it colonizes open fields and roadsides. Its ability to grow in poor soils, fast growth, ornamental foliage and fragrant flowers make for a favorite tree to plant.

More on Black Locust

Black locust is sometimes called yellow locust and grows naturally on a wide range of sites but does best on rich moist limestone soils. Black locust is not a commercial timber species but is useful for many other purposes. Because it is a nitrogen fixer and has rapid juvenile growth, it is widely planted as an ornamental, for shelterbelts, and for land reclamation. It is suitable for fuelwood and pulp and provides cover for wildlife, browse for deer, and cavities for birds.

We must recognize that black locust is not an important tree for logging purposes as there is very little timber value and it has little lumber or paper pulp potential. We still need to remember that the tree has and is used in the United States to be manufactured into a wide variety of products.

Robinia pseudoacacia is planted for many specialized purposes. Black locust is used for fence posts, mine timbers, poles, railroad ties, insulator pins, ship timber, tree nails for wooden ship construction, boxes, crates, pegs, stakes, and novelties. Pulp with satisfactory mechanical properties can be made from the tree, particularly by the sulfate process but commercial value awaits further investigation.