Honey Locust Leaf Identification: Leaflets, Thorns, Pods

Honey locust leaves are compound and fern-like: a central stalk carries many small, oval leaflets, and on vigorous young trees the leaf divides a second time, so the leaflets sit on side branches of the stalk. Wikipedia describes the leaves as pinnately compound on older trees and bipinnately compound on vigorous young ones, with leaflets 1.4 to 3.6 cm (1/2 to 1 1/2 in) long. The University of Minnesota's tree guide adds that the leaves are alternate and that the leaflets are ovate, green in summer and yellow in fall; Wikipedia's range for the fall colour runs from cream and tan to golden yellow.

TreeIdentifier's guide counts 14 to 30 leaflets on a once-compound leaf, each about 3/4 to 1 inch long. Both leaf forms can grow on the same tree, so do not be put off if two branches look different.

The most common mistake is to treat a single leaflet as a whole leaf. A leaf starts at a bud on the twig, a point the Footsteps in the Forest leaf gallery stresses for all compound leaves. Find the bud, and everything beyond it, stalk and leaflets together, is one honey locust leaf.

• Thorns. Wild honey locust carries thorns 6 to 10 cm (2 1/2 to 4 in) long, sometimes 20 cm (8 in), often branched into several points and grouped in dense clusters (Wikipedia). TreeIdentifier compares a cluster to small antlers: one main spine with 2 to 4 shorter ones. Many planted street trees are the thornless form, Gleditsia triacanthos f. inermis, which the University of Minnesota says is the one recommended for urban planting, so a missing thorn does not rule the tree out.
• Bark. Red-brown on young trees, gray-brown later, and broken into long strips with raised edges (University of Minnesota).
• Flowers. Small greenish clusters in late spring with little ornamental value (University of Minnesota); Wikipedia says they are strongly scented, in clusters 3 to 7 cm long.
• Pods. Flat, reddish brown, often twisted, 7 to 35 cm (3 to 14 in) long and 1.5 to 3 cm wide, holding a soft, slightly sweet pulp (Wikipedia, University of Minnesota). TreeIdentifier notes they often hang on the tree through January or February, which makes them a winter field mark.
• Size. The University of Minnesota gives 60 to 80 ft in height and spread; Wikipedia gives 20 to 30 m and a life span of up to about 125 years.

Honey locust and black locust (Robinia pseudoacacia) are both called locust and both have compound leaves, but they belong to different genera and the leaves differ in every measurement. Figures below are from Wikipedia's articles on each species.

• Leaflet number. Black locust: 9 to 19 leaflets on a leaf 15 to 36 cm long. Honey locust: many more, smaller leaflets, and often a twice-divided leaf; black locust leaves are only once compound.
• Leaflet size and tip. Black locust leaflets are 2.5 to 5 cm long and 0.6 to 2 cm wide, rounded or slightly notched at the tip. Honey locust leaflets are 1.4 to 3.6 cm long.
• Thorns. Black locust has a pair of short spines, up to 2 cm, at the base of each leaf, triangular with a flared base and dark purple. Honey locust thorns grow on the branches and trunk, much longer, and branched.
• Flowers. Black locust has showy, very fragrant cream-white flowers with a yellow blotch, in May or June for 7 to 10 days. Honey locust flowers are small and greenish.
• Pods. Black locust pods are 5 to 10 cm long with 4 to 8 seeds; honey locust pods are 7 to 35 cm long.

The quickest single test: look at the base of a leaf. A pair of short spines there means black locust; long branched thorns on the wood away from the leaves mean honey locust.

• Honey locust (Gleditsia triacanthos) - fern-like, often twice-compound leaves with tiny leaflets, branched thorns on the wood, pods up to 35 cm with sweet pulp.
• Thornless honey locust - the same species, form inermis; same leaves and pods, no thorns. Common on streets and in parking lots.
• Black locust (Robinia pseudoacacia) - once-compound leaves with 9 to 19 larger, round-tipped leaflets, paired spines at the leaf bases, fragrant white flower clusters, pods 5 to 10 cm. Wikipedia lists it as invasive in several US states. Our black locust wood page covers the lumber.
• Water locust (Gleditsia aquatica) - a close relative of honey locust in swamps of the southeastern US, from Florida west to eastern Texas and north to Illinois. Wikipedia notes its pods usually hold only one seed, a quick way to separate it from honey locust's long many-seeded pods, and that the two species hybridise where they meet.

If leaves, thorns and pods disagree, photograph all three and compare them against the list above rather than relying on the leaf alone.

• Thorns. Wild-type trees carry long, sharp, branched thorns; the University of Minnesota names them as the reason the thornless form is planted in cities.
• Pests and diseases. The University of Minnesota lists honeylocust plant bug, spider mites, leaf spots and canker. Wikipedia adds that thornless cultivars are especially susceptible to the mimosa webworm.
• Pods. Pods up to 35 cm long end up on lawns and paving; TreeIdentifier notes they can hang on the tree into January or February before they fall.
• Spread outside its range. Wikipedia reports that it forms thickets in Australia and has invaded native grasslands in Argentina; TreeIdentifier also lists parts of Europe and South America.
• Size. At 60 to 80 ft tall and wide (University of Minnesota), it needs room.

On the plus side, the University of Minnesota says it tolerates alkaline and clay soils, dry sites, road salt, wet sites and occasional flooding, which is why it is so common along streets. Its wood is dense and rot-resistant (Wikipedia) and has been used for fence posts, railroad ties, pallets, tool handles and fuel (University of Minnesota).

Wikipedia describes honey locust pod pulp as slightly sweet and eaten by wildlife and livestock, while it describes black locust bark, leaves and wood as toxic to people and livestock. Because the two trees share a common name and grow in the same places, do not eat or give anyone any part of a locust tree on the strength of a web page or an app result. Have the tree confirmed by a local extension office or botanist first. If a child or pet swallows pods, seeds, bark or leaves and shows any symptoms, call Poison Control (1-800-222-1222 in the US) or a doctor or veterinarian.

WoodLens identifies honey locust from a photo of the leaf, the bark or a board,. Photograph a whole leaf from the bud outward, a thorn cluster if there is one, and a pod.

This page was drafted with AI help, and every fact was checked against the sources listed on the page.