The Black locust (Robinia pseudoacacia) is a medium to large deciduous tree with contorted upper trunk and branches. Leaves are compound, consisting of 7-19 leaflets. Fall color is minimal, yellow to gray-green. Twigs zigzag and are brittle with thorns. Bark on young trunks soon develops scaly ridges. Mature trunks are extremely rugged with deep furrows and interlacing ridges. Flowers are showy, pea-like, white, and hang in clusters after leaves in late spring. Fruits are flattened pods that ripen in fall and can persist into winter. The tree is able to reproduce via seed or by root suckers. Native to parts of the central and eastern United States, black locust is commonly cultivated and now widely naturalized in much of North America and elsewhere. One of the world’s most adaptable, tough, distinctive, and familiar trees. The wood is very durable but attacked by borers in much of North America, but not in the West. Introduced to Europe in 1601. British colonialists in America discovered the species in 1607 at Jamestown, Virginia. American Indians made bows from the strong flexible wood and cultivated the tree for this purpose. Colonialists used the wood in shipbuilding. Robinia sometimes confused with Gleditsia which has bipinnate leaves and thorny trunks. In contrast, Robinia is only pinnate. Robinia genus named in honor of Jean and Vespasien Robin who were sixteenth century herbalists to the French Royal Household
Common name: Black Locust, Yellow Locust, Locust
Scientific Name (family and order): Robinia pseudoacacia L. (Fabaceae, Fabales)
Species Origin: Southeastern United States
New Jersey Status: USDA Native
Habit: 80’ high x 50’ wide. The bole has a 3’ diameter. Broadly columnar.
Habitat: Zones 3 -8; woods and thickets, a ready colonizer of open fields.
Trunk/Stem: Bark gray brown, deeply furrowed with scaly ridges. Mature trees produce root suckers which may rise up to 30’ away from the trunk. Twigs may have paired 1/2″ stipular spines on branchlets.
Leaves: Deciduous, Pinnately Compound, Alternate. Pinnate 12” long with 11 to 21 elliptic to ovate, untoothed leaflets, each 2” long, often indented at the apex and ending in a slender point; adaxial blade surface blue-green; abaxial blade surface gray-green and thinly hairy becoming smooth with maturity. The shoot (the petiole) often with two spines at the base of each leaf (stipular). The entire leaf is 11” long.
Flowers: Perfect. Pea-like (5 unequal parts), ¼” long white with yellow green blotch petals, with reddish brown calyx having 5 teeth; flowers, fragrant, hang in dense racemes 8” long, blooming in early to mid-summer.
Fruits and seeds: A smooth, dark brown hanging pod, 4” long. The pod opens in late summer to yield 3 – 14 smooth black-brown, kidney-shaped ¼” wide seeds. But seed pods may persist over winter.