Honey locust is a medium-sized tree with a short, thorny trunk, thorny branches, and a loose, open crown.
Leaves are alternate, compound, 5–10 inches long, with 15–30 leaflets; leaflets ¾–2 inches long, broadest near the base to even throughout; margin entire or sometimes with very small, round teeth; upper surface shiny; lower surface paler, often hairy.
Bark is grayish brown to black, on older trees with grooves deep, narrow, separating into scaly ridges with sides or ends free and curved outward; often bearing heavy, simple or branching spines.
Twigs are greenish or reddish brown, shiny, stout, often zigzag, with solitary or branched spines that are rigid, sharp, straight, shiny, purplish brown, up to 12 inches long.
Flowers May–June; greenish white; male flowers in catkins, female flowers in clusters; found on separate trees or sometimes as a complete flower.
Fruit a dark brown, leathery pod, 6–18 inches long, narrow, flat, twisting at maturity; seeds 6–27, brown, oval, about ½ inch long.
Height: to 60 feet.
Statewide.
Habitat and Conservation
Occurs in bottomlands along streams and their valleys, also upland slopes and open or wooded pastures.
It is a common invader (or pioneer species) of pastures and idle fields, and it is troublesome for farmers whose tractor tires the thorns puncture.
Honey locust, and trees such as eastern red cedar, wild plum, and persimmon, are some of the first woody plants to grow in places where forests have been cut down, and their establishment is one of the early steps in that land reverting back to a woodland or forest community.
Status
Native Missouri tree. Some thornless cultivated varieties are popular landscaping trees. Natural trees, heavily covered with large, sharp thorns, are often considered a nuisance when they grow near people.
Human Connections
Cultivated thornless and seedless varieties of honey locust are popular in landscaping and along city streets — in autumn, the small leaflets turn bright gold before blowing away in the wind, and the leaves' little midveins make little mess. The rather open canopy of honey locust creates a dappled shade that allows lawn grasses to flourish below.
Native Americans ate the fleshy sweet pulp of the young pods, and the pods and inner bark have been used medicinally in the past.
The species name, triacanthos, means "three thorns" and refers to the thorns, which frequently branch into three sections. The sweet pulp around the seeds account for the "honey" in the tree's name.
In several parts of the world, such as Australia and South America, where it is not native, people have introduced honey locust, and it has proven to be highly aggressive and invasive in those regions. Even where it grows natively in North America, honey locust is frequently considered an unwelcome pest species.
Cattle relish the sweet pods, when they are on the ground, but the spines prevent the animals from nosing into the trees and browsing the foliage. This is one reason why honey locusts are successful invaders in pasture land. Another is that cattle tend to excrete the undigested seeds, spreading the offspring away from the parent tree.
The wood of honey locust is very durable and tough. One sign of its toughness is when you see an old, mostly dead honey locust standing solidly on a pasture (or on a streetside or island in a parking lot), with little sign of rot.
Ecosystem Connections
The seeds and pulpy pods provide winter food for rabbits, squirrels, and deer.
The flowers are reportedly a good bee food.
Honey locust is a top food plant for caterpillars of the honey locust moth, bisected honey locust moth, silver-spotted skipper, moon-lined moth, and the orange wing. These caterpillars, and the winged adults, are important foods for birds.
Honey locust is a “pioneer” or early colonizing species, one of the first kinds of trees to become established in disturbed landscapes such as old fields and pastures that are reverting back to forest.
Honey locusts cannot tolerate fire; historically, honey locusts and similar woody pioneer species were prevented from gaining a foothold in native prairies, savannas, and glades by periodic fires. Such fires were ignited by lightning or were set by Native Americans.
Why the enormous thorns? One hypothesis is that the thorns evolved to deter large Pleistocene mammals (megafauna), such as mastodons, from feeding destructively on the foliage and branches. These now-extinct animals may also have played important roles in distributing the undigested seeds of honey locust, Kentucky coffee tree, and Osage orange, after swallowing the fruit.
From June into September, and especially in late August, you might see the foliage of honey locusts clumped together and turning a brownish, burnt orange. Sometimes almost all the outer leaves of the tree's crown are affected. Upon closer inspection, you'll see there's a silken webbing holding the leaves together. This is most likely the mimosa webworm (Homadaula anisocentra), a nonnative moth first recorded in the United States (in Washington, DC) in 1943. The insect's range has been expanding. Its primary food plant is mimosa (which is also nonnative), but our native honey locust is its second-favorite host in America. University of Missouri Extension and Bridging the Gap have helpful pages about this nonnative moth.
