Black Locust Tree Identification: Spines, Leaves, Pods

Black locust is identified by a pair of short spines at the base of each leaf and a long compound leaf of small oval leaflets with smooth edges. The Missouri Department of Conservation (MDC) gives leaves 8 to 14 inches long with 7 to 19 leaflets, each 1/2 to 2 inches, and describes the twigs as dark brown, stout and zigzag, with a pair of small spines where the leaves attach. NC State Extension gives the spines up to 1.25 inches.

The bark is the other strong clue. MDC describes it as reddish-brown to almost black, with deep grooves and long, flat-topped ridges that interlace. Tree Identifier compares it to braided or twisted rope.

In late spring the tree is easy: MDC records fragrant, white, pea-shaped flowers in loose drooping clusters 4 to 5 inches long in May and June, with a yellow blotch inside the upper petal. After that come flat, smooth, reddish-brown pods 3 to 5 inches long holding 4 to 8 seeds, which often hang on through winter (MDC).

The two share a name but are easy to separate. From MDC's field guides for each species:

• Thorns: black locust has a pair of small spines at each leaf base. Honey locust has rigid, shiny, purplish-brown thorns, single or branched, up to 12 inches long, often in clusters on the trunk. Many planted honey locusts are thornless cultivars (Tree Identifier).
• Leaves: black locust leaflets are 1/2 to 2 inches and number 7 to 19. Honey locust leaves carry 15 to 30 leaflets 3/4 to 2 inches, and Tree Identifier notes they can also be twice-compound with a fern-like look.
• Flowers: black locust has showy white hanging clusters. Honey locust flowers are greenish-white and inconspicuous, male and female on separate trees.
• Pods: black locust 3 to 5 inches, flat and smooth. Honey locust 6 to 18 inches, dark brown and leathery, twisting as they mature.
• Height: MDC gives black locust to 70 feet and honey locust to 60 feet.

MDC lists other look-alikes for both trees: Kentucky coffee tree, American yellowwood, mimosa, eastern redbud and lead plant.

NC State Extension rates black locust's poison severity as high, lists the bark, leaves and seeds as poisonous, and names the toxic compounds robin, robitin and robinine. Symptoms it lists include depression, weakness, dilated pupils, vomiting, bloody diarrhea, weak pulse, cold arms and legs, and shock. MDC goes further and states that all parts of the tree are considered toxic. Wikipedia notes the bark, leaves and wood are toxic to both humans and livestock.

Some foraging guides, including one of the top search results, describe eating the flowers. Because the government and university sources consider the tree toxic, this page does not recommend eating any part of it. If a person swallows bark, leaves, seeds or pods, call Poison Control at 1-800-222-1222; for livestock or pets, call a veterinarian.

On touching the tree: the sources above describe poisoning by eating, not by contact. The spines can puncture skin, so wear gloves when cutting or handling branches, and see a doctor if a puncture becomes red or swollen.

Black locust is native to two areas: the Appalachians from Pennsylvania to northern Georgia, and the Ozark Plateau and Ouachita Mountains of Arkansas, Oklahoma and Missouri (Wikipedia). Outside those areas it spreads aggressively:

• Root suckers: MDC notes it easily invades disturbed sites, often forming clones from sucker sprouts, and is difficult to eradicate once established. Wikipedia describes dense colonies that shade out other species.
• Invasive listings: Wikipedia notes it is listed as invasive in Connecticut, Wisconsin and Michigan and prohibited in Massachusetts; NC State notes it has become invasive in the Midwest.
• Pests: NC State lists the locust borer, often fatal, and the locust leaf miner, which browns the foliage.

The same traits make it useful: its roots fix nitrogen, letting it grow on poor soils (Wikipedia), and the wood is very hard and rot-resistant, with a Janka hardness of 1,700 lbf and flavonoids that let it last over 100 years in soil (Wikipedia). MDC ranks it the seventh-hardest wood of any North American tree.

Research and drafting for this page used AI assistance. Every measurement, date and claim was then checked against the sources listed below, which were opened and read on 2026-09-25. Where two sources give different numbers, both are shown.