Invasive Plants of Wisconsin
Black Locust has alternate compound leaves with blunt entire leaflets. The paired, stout thorns at each node are unlike any other tree in our area except for Prickly Ash, which has pointed leaflets and is likely to be recognized as a shrub. Prickly ash also tends to have at least a few small thorns on the midrib of many leaves and Black locust has no thorns on the leaves. The buds of Black Locust are hidden beneath the bark of the twigs and buds of Prickly Ash are clearly visible. The flowers of black Locust are white and very aromatic and the fruit is easily recognize as a legume.
The native range of Black Locust was probably limited to southern Wisconsin, but it has been widely planted and sometimes escapes on disturbed sites as far north as Douglas and Bayfield Counties. It can cause serious problems as an invasive species.