I was pleasantly surprised when I stumbled across some black locust trees by a church parking lot in Austell, Georgia. One large tree had a freshly broken limb, and smaller trees thickly ringed the parking lot below it. As I rummaged around taking pictures, I had to be careful not only of the thorns but for the possibility of snakes. Perhaps the thorns and thickets were a weak attempt to defend itself, as the black locust is more severely damaged by insects and disease than any other eastern hardwood species. I feel lucky to have found such a large, healthy tree.
The black locust, Robinia pseudoacacia, is native to the central Appalachian and Ozark mountains of North America. This tree was named after the person credited with being the first to 
plant the tree in Europe, in 1601. Eocene and Miocene fossils in Europe indicate this tree once existed there, so Robin was actually re-introducing the tree to Europe. The black locust has now spread over most of North America and around the world, due to both its desirable qualities and its invasive nature.
The black locust can grow to over 100 feet in height. It may grow as much as 6 feet in a year 
when young. Though the tree produces seeds, it spreads primarily by root suckers forming thorny thickets. It is considered an invasive species in many areas, but due to damage by insects and disease it may only develop to exist as thorny shrub thickets. The tree is shade intolerant and spreads only to shade or natural barriers. The heartwood is considered as durable as pressure treated wood, and this wood is considered the hardest and strongest wood in the Eastern United States. However, attack by insects and diseases makes timber production difficult. The tree has a trunk that is relatively straight. Branches are stiff and brittle, forked and crooked, and may break in high winds. The trunk, branches and twigs may or may not have thorns, which appear in pairs at leaf buds. They may be an inch long. The bark is gray or 
light brown, and thick and heavily ridged and furrowed. Pinnately compound leaves are on an 8 to 14- inch long stem. The 7 to 19 oval leaflets on the stem are about one inch long and arranged alternately. Leaflet edges are smooth.
The fragrant flowers of the black locust are perfect, having male and female parts. They hang in wisteria- like clusters 4 to 8 inches long blooming in May or June, and are pollinated by bees and hummingbirds. Individual flowers have 5 white petals with a yellow spot on the top petal. They are about ¾ inches long, and resemble pea flowers. The fruit is a thin green pod, 2 to 4 inches long, containing 4 to 8 small and smooth white kidney-shaped seeds. In the fall, the ripe 
pod turns light brown and the seeds turn red- brown. The seeds may lie dormant where they fall and sprout years later.
The black locust tree has had many uses. With its attractive form, its sweet- smelling clusters of pretty white flowers, and its delicate foliage casting a thin, pleasant shade, it is a great ornamental. The tree is used where strength and durability is important, such as for fence posts, train rails, flooring, furniture and pegs. Indians used the wood to make strong bows. It is said that black locust pegs helped win the decisive battle of the War of 1812 on September 11, 1814 on Lake Champlain, by keeping the siding on American ships from coming apart. Cannon balls inflicted more damage on British ships which used white oak pegs. Black locust 
flowers are important to bees for making honey. Flowers are also edible, and may be eaten raw or in culinary dishes. The young green seed pods are considered by some to be edible, but I have not tried them. The seeds in the green pods are edible, and to me they taste much like green peanuts. They are small and tedious to gather, and not worth the trouble for serious eating. Any other parts of the tree are not edible, and for those parts mentioned as edible anyone with food sensitivities should not try to eat any part of the tree.
The black locust is a nitrogen fixing tree and is sometimes used for reclamation of damaged land, adding organic matter and nitrogen to the soil. Fibrous roots help hold the soil preventing erosion. Black locust firewood burns slowly and at a very high temperature, similar to anthracite coal. This tree has served many important purposes.
The black locust tree is an interesting tree with an interesting history. Despite its invasive nature, it has many great qualities. This tree would be used much more often if it were not so susceptible to damage by insects and diseases.