black locust (Robinia pseudoacacia) — identification, habitat & look-alikes

Black locust is a tree native to parts of the Appalachians and Ozarks that now grows across the contiguous United States after widespread planting. Its fragrant white flowers hang in clusters in spring to early summer, and new shoots from its roots can form dense thickets.

Appearance

Appearance: This deciduous tree is commonly 30–50 ft (9–15 m) tall. Young twigs often carry paired, short spines at the bases of the leaves.
Leaves: Each has 7–19 rounded or oval leaflets.
Flowers: Fragrant white, pea-shaped flowers hang in clusters in spring to early summer.
Fruit: Flat brown pods hold several hard seeds and often remain on the tree into winter.

Look-alikes

Japanese pagoda treeStyphnolobium japonicum

Japanese pagoda tree flowers in midsummer with large, branched clusters and later makes pods pinched between the seeds. Black locust has drooping white flower clusters in spring and flat pods.

Why they get mixed upBoth are legume-family trees with leaves made of many leaflets.

bristly locustRobinia hispida

Bristly locust is usually a 2–10 ft (0.6–3 m) shrub with pink flowers and purple-brown bristles on its stems. Black locust is a much taller tree with white flowers and no dense stem bristles.

Why they get mixed upBoth plants have similar leaves and hanging flower clusters.

Where it lives

Typical habitats: roadsides
old fields
woodland edges
Range: Its original U.S. range centers on parts of the Appalachians and Ozarks, but it now grows across the contiguous states after widespread planting.
Preferred conditions: It grows fastest in full sun on open, disturbed ground and tolerates many soil types.

Growing it

Propagation: It reproduces by seed and spreads vigorously through and stump sprouts.
Toxicity: The bark, leaves, and seeds contain toxic compounds and should not be eaten.

Conservation

IUCN Red List: LCLeast ConcernLow risk of extinction
Threats: Outside its original range, dense clonal stands can shade out plants of open habitats.

Culture and stories

Culture and stories: The tree was widely planted for erosion control, fence posts, and its durable wood.
Its flowers are valued by beekeepers, but its spreading roots can make it difficult in small landscapes.

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