- What Are the Dangers of Black Locust Tree Thorns?
- Toxic Tree
- Walkway Hazard
- Inflatable and Plastic Equipment
- Wildlife Habitat
- About Locust Trees Bean Pods
- Honey Locust Pods
- Black Locust Pods
- Other Locust Pods
- Arkansas Trees
- Unique Trees
- Plant of the Week: Locust, Honey
- Honey LocustLatin: Gleditsia triacanthos
- How to Identify Tree Thorn
What Are the Dangers of Black Locust Tree Thorns?
The black locust tree (Robinia pseudoacacia), also called false acacia, grows in U.S. Department of Agriculture plant hardiness zones 3 to 8. In addition to its usefulness as a shade tree, black locust features attractive springtime blossoms and a pleasant fragrance. The thorns that grow in pairs below the leaves serve as protection for the tree, but can be potentially dangerous in your yard.
All parts of a black locust are extremely toxic and can cause severe stomach pain or death in children, pets and livestock if eaten. This is especially problematic with livestock — particularly cows and horses — which often graze on tree leaves. The thorns grow on branches at the base of a cluster of leaves, so it would be easy for an animal to eat the thorns while also taking a bite of leaves. The leaves are also toxic, but in addition to thorn toxicity is the problem of extreme pain when swallowing thorns that grow up to 2 inches long. Keep livestock well away from black locust. If you want to attract grazing deer or other animals to your yard, don’t plant black locust.
A black locust planted too close to a walkway or high-traffic area of your yard could easily scratch or poke at passersby. Although being scratched by the tree isn’t poisonous, because it’s only toxic if eaten, those sharp barbs can certainly hurt. A young child at eye level to a black locust tree canopy could get poked in the eye. The thorns don’t grow along the trunk, so this is mostly problematic with young trees. Beware fallen branches, because the thorns can easily poke through a thin shoe sole.
Inflatable and Plastic Equipment
Inflatable toys, pools, plastic water slides, bounce houses and other equipment keep kids busy outdoors, but black locust thorns can bring the fun to an abrupt end. Branches can fall out of the trees on windy days and easily tear holes in the thin, plastic material used to make these items. Even pools and ponds with rubber liners can be punctured if a locust branch with thorns falls in the water. Puncture holes can also happen if you place the equipment in the yard without first checking for fallen thorny branches. Anchor inflatable equipment to the ground so it doesn’t get caught in the wind and blown into a small black locust tree, where it can snag on the sharp thorns.
Birds often rely on thorny bushes and trees to provide protected shelter. While you might welcome some new avian residents to your garden, black locust trees might also invite nuisance birds such as crows. Crows scare away other birds and can also devour a vegetable garden well before you have a chance to harvest. If you want to keep black locusts on your property while discouraging bird pests, cover crops with bird netting. Alternatively, install lots of birdhouses to invite a martin bird colony to your yard — these birds won’t destroy your garden and help keep crows away.
About Locust Trees Bean Pods
Many varieties of locust grow in the U.S., with honey locust and black locust being most common. Honey locust has pods that contain edible seeds, while the pods of other locust tree varieties are primarily for reproductive use.
Honey Locust Pods
Honey locust (Gleditsia triacanthos) grows up to 80 feet tall. Its pods are flat and shaped like a strap. Lime color in the summer and and reddish-brown in the fall, the pods are 12 to 18 inches long and contain 12 to 14 seeds. The pods are eaten by many animals, including deer, cattle, squirrels, rabbits and birds.
Black Locust Pods
Black locust (Robinia pseudoacacia) is a medium-size tree that grows up to 80 feet tall. Its pods are dark brown and approximately 4 inches long. They stay attached to the tree during winter. Each pod has up to 14 seeds, which are poisonous to humans.
Other Locust Pods
New Mexican locust (Robinia neomexicana) is a small tree that reaches approximately 25 feet tall. It has flat, brown pods 2 to 4 inches long that are covered in gland-tipped hairs. Bristly locust (Robinia hispida) grows to a height of approximately 8 feet and has flat, bristly pods that are 2 to 2-1/2 inches long.
The young greenish-brown pods that appear from mid-summer into early fall yield a sweet treat, whereas the older twisted maroon-colored pods that fall in winter tend to be bitter, although it’s possible to find a few older ones that contain good stuff. Unfortunately, the young pods are virtually inaccessible, being protected as they are by the tree’s vicious three-forked spines.
A squirrel being chased by a dog will flee up a honey locust tree because of these barbs, which cluster around the area where the first set of limbs grow as well as along the limbs. The larger spines can be up to 12-inches long!
My friends and I were foolish fellows, but never so crazy as to climb a honey locust tree. We used to occasionally find pod clusters that could be reached from the ground or an adjacent tree or building. Usually, however, we attached a rope to a rock and tossed it over a limb and stripped off the fruits by pulling the rope across them.
I suppose the last time I harvested honey locust that way was in the mid-1950s. Now, I like to pick up the fallen pods and keep them around my desk or add them to dried arrangements.
Recently, I decided to read up on honey locust (Gledistia triacanthos), which grows typically to about 75 feet beside roads and fields here in WNC, but sometimes in the forest. Here are some things I found:
• The “Knowing Your Trees” volume first issued by the American Forestry Association in 1937 advises, “While belonging to the pea family, botanists (do not) classify it with … black locust (Robinia pseudoacacia), with which it is often confused … In 1753 Linnaeus named the genus ‘Gledistia’ in honor of Johann Gottlieb Gleditsch, then professor of botany at Berlin. The forked spines are recognized in ‘triacanthos,’ meaning ‘three-thorned’ … The numerous, brown, oval bean-like seeds enclosed within the pods are separated by a sweet and succulent pulp. They are eaten by cattle, deer, rabbits, foxes and squirrels, which scatter the seeds over large areas … The species matures at about 120 years, but may live longer.”
• In “The Common Forest Trees of North Carolina” (1977) pamphlet issued by the N.C. Department of Natural Resources states that the wood, which has been used for fence posts and railway ties, is “coarse-grained, hard, strong, and moderately decay-resistant. It should not be confused with the very durable wood of the black locust.”
• In Fall Wildflowers of the Blue Ridge and Great Smoky Mountains (1987) Oscar Gupton and Fred Swope note, “Honey locust, also known by the names sweet locust and honeyshuck, is very much an ornamental species by way of its large and colorful fruits and the finely divided foliage that produces an effect of green, lacelike mist. The formidable thorniness has a beauty of its own, but it can also present formidable problems. There is, however, a (cultivated) form of the tree that is completely free of thorns.”
• L.A. Peterson in Edible Wild Plants (1977) volume in the Peterson Field Guide series warns that the shorter, bulkier pods of the Kentucky coffee tree (Gymnocladus dioica) — occasionally found in WNC around old homesites — are poisonous when fresh, although they are used as a caffeine-free coffee substitute when roasted and ground.
• If you find grasshopper or small rodents impaled on honey locust thorns, you’re observing the work of a loggerhead shrike, a stocky black, white, and gray bird that resembles a mockingbird. In Birds of the Carolinas (1980) the authors note that “shrikes are called ‘butcherbirds’ because they hang their excess prey on thorns or barbed-wire fences somewhat the way butchers hang slaughtered animals on meat hooks.”
• My favorite tree-information book is A Natural History of Trees of Eastern and Central North America (1950) by Donald Culross Peattie, who made his home in the Tryon, N.C., area during the period before and after World War II. We’ll give Peattie the last word in our honey locust symposium:
“Down in Florida this tree is still sometimes called by the obsolete name of Confederate pintree, because its formidable spines were used to pin together the tattered uniforms of the southern hosts in the war of the Blue and Gray. Honeyshucks is the name used in some parts of Virginia, and very appropriate it is on account of the sweet pods eaten by cattle and sometimes by nibbling country boys ….
“The word locust, of course, is a transportation to the New World tree of an Old World name. When Saint John went into the wilderness he lived on ‘honey and locusts,’ says the Bible, and by later transposition the name of the noisy insect became attached to the rattling, edible pods of carob (Ceratonia siliqua), often called St. John’s-bread. Not unnaturally, a sweet-tasting pod on an American tree received the name ‘locust.’ While the thorns of the black locust are superficial and easily picked off, those of the honey locust arise from the wood and cannot by any means be pulled out. At first they are bright green, then bright red, and when mature a rich chestnut-brown that shines as if it had been polished. In the days when southern mountain folk had to use the natural resources at hand, they employed these thorns in carding wool, and for pinning up the mouths of wool sacks.”
Description: This tree is 50-100′ tall at maturity, forming a single trunk about 2-3½’ across and an open plume-like crown that is somewhat flattened at its apex. Trunk bark of mature trees is light gray to gray-black and divided into large flat plates with upturned margins; these plates are slightly scaly and they are separated by shallow furrows. The bark of branches and twigs is more smooth, brown, and hairless, while young shoots are light green and pubescent. Alternate compound leaves occur along the twigs and young shoots. These leaves are evenly pinnate or bipinnate and 6-14″ long. Pinnate leaves have 5-11 pairs of simple leaflets, while bipinnate leaves have 4-7 pairs of pinnate leaves that are each divided into 5-11 pairs of simple leaflets. There are no terminal leaflets. The rachis of each compound leaf is light green and pubescent. The leaflets are ¾-1½” long and about 1/3 as much across; they are oblong to lanceolate-oblong and slightly crenate along their margins. The upper surface of the leaflets is yellowish green to dark green and hairless, while the lower surface is more pale and either hairless or minutely hairy. The leaflets have very short petiolules (basal stalklets) that are less than 1/8″ (3 mm.) long. Along the trunk, there are usually both simple and branched thorns up to 8″ long; there are also simple and tripartite thorns along the lower branches. However, there is also a thornless variety (var. inermis) of Honey Locust that is uncommon in the wild, although often cultivated.
The small greenish yellow flowers are produced in racemes about 2-5″ long; they are usually male (staminate) or female (pistillate), although sometimes perfect (both staminate & pistillate). Individual male flowers have a calyx with 5 lobes, 4-5 petals, and 3-10 stamens, while individual female flowers have a calyx with 5 lobes and a pistil with a single style. Individual perfect flowers have both a pistil and several stamens. The blooming period occurs from late spring to early summer for about 2 weeks. The flowers have a sweet fragrance. Fertile female flowers are replaced by flattened seedpods that become 6-14″ long and 1-1½” across at maturity. Mature seedpods are dark brown, hairless, and often hooked or spirally twisted. Each seedpod contains several large seeds that are reniform in shape and about 1/3″ (8 mm.) long; they have hard seed coats. The seeds are embedded in a thick sweet pulp. The seedpods fall to the ground unopened during the late fall or winter. The woody root system has a taproot and abundant lateral roots that are widely spreading and deep. The deciduous leaflets turn yellow during the autumn.
Cultivation: This adaptable tree prefers full to partial sunlight and moist to dry-mesic conditions. It will flourish in almost any type of soil (pH range 6.0-8.0) if it is not too acidic. Both temporary flooding and hot dry weather are tolerated. The root system doesn’t fix nitrogen in the soil. New trees can be propagated by seeds or vegetatively by cuttings. Growth and development is fairly fast; young trees can produce seedpods in as little as 10 years. Longevity of healthy trees is typically 100-150 years. One of the advantages of Honey Locust as a landscape tree is the light shade that is cast by its open crown; this allows the survival of turfgrass and other plants.
Range & Habitat: The native Honey Locust has been found in almost every county of Illinois; it is common. Habitats include upland woodlands, bottomland woodlands, woodland openings, woodland borders, powerline clearances in wooded areas, savannas, edges of limestone glades, thickets, fence rows, pastures, and roadsides. This tree colonizes disturbed areas that are relatively open; it is intolerant of shade. Because of the thin bark, Honey Locust is vulnerable to wildfires. The thornless variety of this tree is often cultivated as a landscape plant; it often escapes in both urban and suburban areas.
Faunal Associations: The flowers are cross-pollinated primarily by small bees and flies. Both nectar and pollen are available as floral rewards to such visitors. The caterpillars of Epargyreus clarus (Silver-Spotted Skipper) feed on the foliage of Honey Locust. Several moth caterpillars prefer this tree as a host plant: Catocala illecta (Magdalen Underwing), Catocala innubens (The Betrothed), Catocala minuta (Little Underwing), Spiloloma lunilinea (Moon-Lined Moth), Sphingicampa bicolor (Honey Locust Moth), and Sphingicampa bisecta (Bisected Honey Locust Moth). Several leafhopper species also prefer this tree as a host plant: Erythridula aenea, Erythridula brundusa, Erythridula clavata, Erythridula diffusa, Erythridula gleditsia, and Macropsis fumipennis (Honey Locust Leafhopper). Other insect feeders include the treehopper Micrutalis clava, Diaphnocoris chlorionis (Honey Locust Plant Bug) and other plant bugs, Anomoea flavokansiensis and other leaf beetles, the larvae of Agrilus difficilis (Honey Locust Borer) and other wood-boring beetles, the larvae of the seed weevil Amblycerus robiniae, and the larvae of Dasineura gleditchiae (Honey Locust Pod-Gall Midge). See the Insect Table for a more complete listing of the invertebrate species that feed on this tree. Some mammals and birds also use Honey Locust as a source of food. The seedpods with their edible sweet pulp are eaten by cattle, sheep, goats, deer, opossums, tree squirrels, crows, starlings, and Bobwhite quail. It is thought that some extinct megafauna of the ice age, including the American Mastodon, also ate these seedpods and helped to distribute the seeds into new areas. Cattle, deer, rabbits, and groundhogs browse on the foliage of seedlings, saplings, or the lower limbs of trees; rabbits also gnaw on the bark of young trees during the winter.
Photographic Location: Busey Woods and other locations in Urbana, Illinois.
Comments: Wild trees are often formidably armed by thorns; it is possible that this functioned as a defense against the American Mastodon and other large megafauna of the last ice age. Today, these thorns discourage squirrels, opossums, raccoons, and humans from climbing this tree. The only other tree that Honey Locust can be confused with in the Midwest is Black Locust (Robinia pseudoacacia). Black Locust has slightly larger leaflets, fewer thorns, shorter seedpods, and more showy white flowers. These flowers have a pea-like floral structure that is typical of species in the Bean family (Fabaceae). The greenish yellow flowers of Honey Locust, in contrast, have a more conventional floral structure.
I recently read that most people, when pressed, can remember a tree that was special to them as a child, whether it was a climbing tree, a Christmas tree or a tree to sit under and read a good book. Trees have the ability to connect us more firmly to a place, as if their roots can entwine us and hold us more firmly than we can ourselves.
When the first European settlers arrived in Arkansas, an amazing 85% of the state was forested. That percentage dropped as more settlers moved into the area and began farming. In the mid-1800s, when the railroad came to Arkansas, that number dropped again, initially with the demand for lumber to lay tracks, and then as the lumber industry blossomed with an easy means of transporting Arkansas timber out of the state.
Fortunately, some of the timber companies had the foresight to practice sustainable forestry early on, and their efforts were augmented by the creation of the Arkansas Forestry Commission in 1931, whose mission it is to protect Arkansas’s forests for all to enjoy. Today, over 50% of the state is still forested and if you stop to look, climb or sit beneath them, you’ll find a wide variety of trees in our state.
It’s Arkansas’s state tree, but Arkansas is home to several different types of pine trees. The shortleaf pine is the most prolific across the state. Sometimes called Yellow or Southern Yellow Pine, it’s a straight, thin tree that drops its branches in a crowded forest, so if you look up, you’ll often see the green needles only near the top of the tree. If you’re south of the Ouachitas, you’re likely to see loblolly pines as well. These fast-growing pines are valued for timber and harvested by many of the major timber companies in southern Arkansas. Both shortleaf and loblolly pines are native to Arkansas.
These solid trees are one of my favorites. Oak trees are the most prolific trees in the state with 29 different variations. Oak trees are often large, broad trees that provide wonderful shade in hot Arkansas summers. The black oak is one of the most common oaks in the state. Its bark darkens into black as it ages and becomes deeply furrowed, like wrinkles on a human face. Its sister tree, the white oak, is slower growing but longer living, sometimes reaching 300 feet. Its bark is an ashy gray and doesn’t wrinkle as deeply as the black oak. Both trees drop acorns in the fall and typically turn red or brown in autumn.
I have a distinct memory of my grandfather sending me outside in the fall to collect hickory nuts to be used in the hickory smoker that would soon yield a delicious turkey or ham on the table. I learned to identify the dark, oval nuts early on. Hickory trees are found alongside the oaks and shortleaf pines that proliferate our Arkansas forests. The black hickory is one of the most common in the Ozarks and Ouachitas, growing easily on mountainsides. Hickory trees have tear-shaped leaves that turn yellow in the fall and the nuts are edible, if you can beat the squirrels to them.
Maple trees are prized for their beautiful fall colors. Red maples are often planted around homes since they grow quickly and display those brilliant red leaves. They are widely distributed across the state. Sugar maples are found in Northwest Arkansas as the southernmost part of a band of trees that extend into the northern and eastern United States. They produce the sap that is famously turned into maple syrup, and although Arkansas is far south of syrup-producing states like Vermont and New Hampshire, you can tap a sugar maple tree here for a short maple syrup season.
Oaks, maples, pines and hickories are all easily found across our state, but here are a few more unique trees to look for on your next venture outdoors.
Also called bois d’arc and hedge apple, Osage orange is fairly easy to spot because of its large green fruit that falls from the tree in September and October. I remember kicking or throwing these “horse apples” around as a kid to see if they would bust apart. The tree is also covered in thorns. Before the use of barbed wire fences, farmers often planted the tree in rows to form a thick, thorny barrier. The tree is originally native to southwest Arkansas, but it can now be found across the state.
This one is fun to look for while hiking. The tree is small and shrub like, and the thin trunk is covered in sharp spines. It literally looks like a thorny walkingstick. It produces purple to black berries in the fall which can cause intestinal discomfort in humans but which are highly prized by bears, so keep an eye out as you walk through the woods.
As its name suggests, the chinaberry tree is not native to Arkansas or the U.S. It was imported from Asia around 1830 and planted across the country as an ornamental tree. Its branches spread out to form an umbrella and in the spring it boasts clusters of beautiful purple flowers. It’s a hardy tree with abundant fruit that birds love to eat, enhancing the tree’s ability to rapidly spread across an area. Though people love the look of the chinaberry tree, it’s considered an invasive species in many states.
Would you like to learn more about Arkansas trees? Author Dwight D. Moore published his field guide, Trees of Arkansas, in 1950. The book was updated in 2014 and is available for purchase from the Arkansas Forestry Commission for only five dollars. Now get outside and enjoy one of Arkansas’s most valuable and beautiful resources.
Plant of the Week: Locust, Honey
The University of Arkansas System Division of Agriculture does not promote, support or recommend plants featured in “Plant of the Week.” Please consult your local Extension office for plants suitable for your region.
Latin: Gleditsia triacanthos
Today’s nurserymen only grow thornless and fruitless honey locust trees.
Most of us live an insulated life, often knowing more about the personal lives of royalty, politicians and movie stars than we do our neighbors. Sometimes we find out almost by accident that someone we’ve known for a long time has an interesting and intriguing personal history.
The same thing happens in the plant kingdom.
Honey locust (Gleditsia triacanthos) is a native deciduous tree of the legume family native to our eastern woodlands. It’s capable of reaching up to 100 feet tall in a deep bottomland site, but it’s usually half that size. It has an oval form with major branches arising low on the trunk.
The most distinctive thing about honey locust is its armament. Stout, usually three-branched thorns grow in clusters arising directly from the trunk and reach 6 inches to 10 inches long. On older thorns, leaves occasionally appear, telling us that these strongly attached thorns are modified branches. Only thornless selections (var. inermis) are used in the nursery trade.
Honey locust leaves are mostly pinnately compound with 20 or so 3/4-inch long oval leaflets. Fall color is a clear yellow. Part of the popularity of honey locust is the fact that the foliage canopy of even large trees is open, allowing filtered sunlight to reach the ground and making it easy to grow a lawn beneath the tree.
The greenish white, sweet scented pea-shaped flowers appear in May high in the tree and are hardly ever noticed. Wild trees produce foot-long, irregularly curled, sweet tasting bean pods that turn dark brown as they mature. In late autumn, they detach and fall in a pile beneath the tree.
Honey locust is called such because of a Biblical reference to the wild honey upon which St. John was said to have subsisted while wandering in the wilderness. The Biblical reference is to the carob tree (Ceratonia siliqua) which has a fat, sweet tasting bean pod. In 1633, Gerard mentions the carob tree is sometimes called locust and also grows in Virginia, an obvious reference to honey locust.
Today, we don’t think of eating tree pods, but before sugar cane became a staple crop, carob fruit was a common sweetener in the Mediterranean region. Excavations of slave quarters in North Carolina found the most common plant refuse to be honey locust seeds, indicating its use as a sweetener.
An even earlier use of honey locust is reported by the Cherokee Tribe. Hollywood gave the impression native Americans used just bow and arrow, but like their South American counterparts, they also hunted with blow guns for birds and small game. They used darts from honey locust thorns with wadding from the down of milkweed pods.
The impressive thorns on the trunk of honey locust probably played a role in the survival of large trees. As recent as 20,000 years ago, mammoths roamed North America, and the sweet sap of this tree was probably a favorite food.
Honey locusts are good, fast-growing, yet strong-wooded shade trees with a useful landscape form. The nursery trade only propagates thornless, fruitless (male) trees, so homeowners need not worry about sharp spines or messy piles of pods. They’re easy to transplant and survive in a wide array of sites. Once established, they have considerable drought tolerance.
In northern states, honey locusts were over planted when elms began dying of Dutch elm disease. Because they were so widely used, pests began to be problematic, and the tree has lost some of its allure in suburbia. Canker diseases, trunk borers and webworms are the most common pests.
By: Gerald Klingaman, retired
Extension Horticulturist – Ornamentals
Extension News – November 24, 2006
The University of Arkansas Division of Agriculture does not maintain lists of retail outlets where these plants can be purchased. Please check your local nursery or other retail outlets to ask about the availability of these plants for your growing area.
How to Identify Tree Thorn
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Several common trees have thorns. Thorns are a defense mechanism evolved by them and are actually modified branches. You can tell these thorn trees apart by examining various aspects of their appearances. Hawthorn, Russian olive, honey locust, Osage orange, American holly, crabapple, and American plums are all commonly found in North America.
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Look at the placement and size of the thorns. Long, straight or slightly curved thorns on the branches indicate a Hawthorn. Short to medium-length straight thorns indicate the Osage orange. Honey locust thorns are branched, and are found in clusters on the trunk. Russian olive tree thorns are found on the ends of its twigs. American plum trees grow thorns on their small branches. Short, rough thorns on the branches are typical of crabapple trees. The thorns of the American holly grow on the edges of its leaves.
Look at how the leaves of the thorn tree are shaped. Oval leaves that are notched or lobed indicate a Hawthorn tree. Oval leaves with smooth edges are typical of Osange oranges. The leaves of the honey locust are several inches long and made up out of two rows of smooth-edged oval leaflets. Russian olive leaves are long, narrow, light green above, gray underneath, and covered with silvery scales. The American plum has serrated leaves with a “V”-shaped base, much longer than they are broad. Crabapple leaves have broad bases, serrated edges and come to a point at the tip. Holly leaves are oval, green, sometimes with brown margins, and have thorns on the edges.
Look at the tree bark’s color, texture and pattern. Hawthorn bark is gray, brown or red. It is smooth on younger trees and becomes scaly as they age. The bark of the Osage orange ranges from gray-brown to orange-brown in color, and is scaly and fissured. Honey locust bark is rough and gray. Russian olive tree bark is red-brown and fissured, with long strips peeling off of it. Young American plums have reddish gray bark with small horizontal ridges. Older plums have gray bark with deep vertical ridges and peeling strips. Crabapple bark tends to be smooth and red to brown in color. American holly has smooth bark when it is young. This bark becomes covered in wartlike growths as the trees age. Holly bark is light gray or white.
Write a list of each aspect of the tree’s appearance. Write the possible candidates next to each item on the list. If most of the features of the tree indicate the same species, then you can be confident that that is the species of the tree that you are studying.