Black locust is a legume with root nodes that, along with bacteria, "fixes" atmospheric nitrogen into the soil. These soil nitrates are usable by other plants. Most legumes have pea-like flowers with distinctive seed pods. Black locust is native to the Ozarks and the southern Appalachians but have been transplanted in many northeastern states and Europe. The tree has become a pest in areas outside its natural range. You are encouraged to plant the tree with caution. Robinia pseudoacacia Links
100 Common Trees
Common Tree Quiz