Locust trees are common deciduous trees found in various landscapes across North America and beyond. These adaptable, fast-growing trees thrive in diverse environments. Many species provide shade and contribute to the ecological balance of their habitats. Understanding their characteristics helps appreciate their role in natural and cultivated spaces.
Thorns on Locust Trees
Some locust tree species possess thorns, serving as a defense mechanism against grazing animals. These protective structures vary significantly between the two most common thorny types: the Black Locust (Robinia pseudoacacia) and the Honey Locust (Gleditsia triacanthos). Thorns are modified stems or branches that deter herbivores.
Black Locust trees feature relatively short, sharp thorns, usually in pairs at the leaf base. These woody, pointed thorns measure 0.5 to 1 inch in length. They appear on young branches and trunks, though mature trees may have fewer or no thorns.
In contrast, Honey Locust trees have distinctive, formidable thorns. These can be quite long, often reaching several inches, some up to 8 to 12 inches. Honey Locust thorns are typically reddish-brown, sturdy, and often branched, appearing on both the trunk and branches. Their size and sharpness make them a prominent identification feature.
Identifying Locust Trees and Thornless Varieties
While thorns are a notable feature, many cultivated varieties, particularly of Honey Locust, are specifically bred to be thornless. The thornless Honey Locust (Gleditsia triacanthos var. inermis) is widely planted in urban settings. Some Black Locust trees also develop fewer thorns as they age.
Beyond the presence or absence of thorns, several other features aid in identifying locust trees. Their leaves are pinnately compound, with many small leaflets along a central stem. Honey Locust leaves can also be bipinnately compound, with leaflets further divided into smaller sub-leaflets.
The bark of these trees also provides identification clues. Black Locust trees typically have deeply furrowed, ridged bark that is dark gray to brown. Honey Locust bark is often smoother when young, developing broader, shaggy ridges with age, and is grayish-brown.
Another distinguishing feature is their seedpods, which are bean-like legumes. Black Locust pods are smooth, flat, and usually 2 to 4 inches long, turning dark brown when mature. Honey Locust pods are longer (6 to 18 inches), flatter, and often twisted, changing from reddish-brown to dark black as they ripen. Their flowers also differ: Black Locust produces fragrant white, pea-like clusters, while Honey Locust has less showy, greenish-yellow flowers.