Black Locust (Robinia pseudoacacia)

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Black locust is a invasive tree that can reach a height of 40 to 100 feet when fully mature. The bark is green and smooth when young and becomes dark brown and deeply furrowed with flat-topped ridges as the tree ages. Seedlings and sprouts grow rapidly and can be identified by long paired thorns. Leaves alternate along the stem. Each leaf is composed of smaller oval to round leaf segments, called leaflets. Leaflets are dark green above and pale below.

Flowers are white with a yellow blotch on the uppermost petal. Fruit pods are smooth and ranges in length from two to four inches. Each pod contains 4 to 8 seeds.

Black locust is originally from southeastern United States and is naturalized throughout the United States and some parts of Europe. Black locust is often found in disturbed areas such as old fields, degraded woods, and roadsides. It was used primarily to anchor soils in construction projects and to stabilize other landforms. It grows best in well drained areas and prefers full sun and little competition.

Black locust can "fix" nitrogen, is a source of nectar for honeybees, produces hardwood lumber, and was used in erosion control and mine reclamation. Some state and federal agencies and nurseries has promoted black locust because of its rapid growth rate.

Black locust produces abundant seeds, but the seeds seldom germinate. Instead, they reproduce through root suckering and stump sprouting. Groves (or clones) of trees grow from damaged roots or stems and are often connected by a common fibrous root system, a characteristic that makes control more difficult.

Outside of its native North American range, black locust poses a serious threat to native sand prairies and oak savannas. Once established, black locust spreads quickly, producing dense clones and shading out other sun-loving plants. Its large, fragrant blossoms also divert pollinating insects from the other plants.

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Last updated: March 22, 2018

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