Black Locust Identification Guide for Western Washington

Black Locust Quick Facts

Scientific name

Robinia pseudoacacia

Also called

False acacia

Tree type

Deciduous broadleaf tree

Leaves

Once-compound, with oval leaflets

Flowers

Drooping white, pea-shaped blooms

Spread

Seeds and shoots from roots

How to Identify a Black Locust Tree

1. Trace one whole leaf. The oval leaflets attach along a central stalk, usually ending with a terminal leaflet. The complete leaves alternate along the woody twig.
2. Look at young twigs. Spines often occur in pairs at leaf bases. They can be especially noticeable on vigorous shoots.
3. Check flowers or pods in season. White pea-like flowers hang in clusters; the later pods are flat and relatively short.
4. Compare the bark. Mature bark has deep, interlacing ridges. Use it alongside the leaf and twig details rather than by itself.

Black Locust Visual Identification Guide

Close-ups help separate features that can disappear in a canopy photograph. The botanical reference images are credited individually. Sound Tree Care photographs show bark and internal wood details from field work.

Leaves: rounded leaflets on one stalk

Leaflets are oval with mostly smooth edges. Many leaves carry roughly 7–19 leaflets, but counts vary. Shape, arrangement, and twig details are more useful than meeting an exact count.

Photograph a complete leaf and where its stalk joins the branch.

Thorns: check the pairs

Black locust commonly has paired stipular spines near leaf attachments. They differ from the large, branching thorn clusters found on many wild-type honey locusts.

Keep your hands clear when positioning a photograph; a sharp spine is useful to see, not to test by touch.

Flowers: hanging white clusters

The typical species produces fragrant white flowers with the characteristic pea-family shape. Look at an individual flower as well as the cluster.

Pink or purple flowering landscape locusts may be other Robinia species or hybrids. Flower color alone does not establish the identification.

Seed pods: flat and relatively short

Pods are generally about 2–4 inches long. They mature from green to brown and can remain after the leaves fall.

Compare their length with honey locust's much longer, often twisted pods. Loose pods may have moved from another tree, so also check the branches overhead.

Bark: deep, interlacing ridges

Older bark becomes thick and strongly furrowed, often with a rope-like appearance. Young stems are smoother.

This close-up records bark texture. A similar texture on another tree is a reason to check its leaves and twigs, not enough to identify it on its own.

Condition: a separate question from species

Sound Tree Care documented internal decay in this particular tree. This does not mean every black locust has the same defect.

Species identification tells you what tree you have. Assessing its condition requires examining the individual tree and the surrounding site.

Black Locust vs. Honey Locust

Both are deciduous trees in the pea family, but they belong to different genera. Compare leaves, flowers, spines, and pods together.

Other Black Locust Look-Alikes

• Tree-of-heaven: pointed leaflets with gland-bearing teeth near the base; papery winged seeds rather than locust pods. See our tree-of-heaven guide.
• Mimosa / silk tree: much finer, twice-compound foliage and pink powder-puff flowers. See our Mimosa guide.
• Ash: whole leaves and buds occur in opposite pairs; its seeds are winged rather than bean-like pods.
• Other ornamental locusts: pink-flowered Robinia selections can resemble black locust. Check more than bloom color or a nursery common name.

Black Locust in Western Washington

Black locust is native to parts of central and eastern North America, not Western Washington. Washington lists it as a Class C noxious weed. King County recommends control, particularly where natural resources are being protected, but does not require it under its noxious-weed program.

New shoots can arise from established roots, creating a group of stems. Cutting alone can stimulate further sprouting. Plan for the roots and follow-up, not only removal of the visible trunk.

1. Confirm the species. Distinguish black locust from honey locust and other compound-leaved trees.
2. Assess the individual tree. Record cavities, cracks, branch attachments, nearby structures, access, and utilities.
3. Define the work. Clarify removal, stump work, debris handling, and who will manage any regrowth.
4. Check local requirements. Confirm applicable ownership and permit questions before work starts.

Where treatment is needed, seek site-specific guidance from your county weed program or an appropriately qualified applicator. Do not assume stump grinding alone will eliminate shoots from roots extending beyond the stump.

Black Locust Identification FAQs