Mystery Plant! #705

John Nelson

Posted Jan. 10, 2023

By John Nelson

It’s the branch of a tree, but this tree is no good for a tree house.

Take a look at the thorns, which can be found up and down the trunk, and also potently arming the branches. You won’t be

Gleditsia triacanthos (Photo by Linda Lee)

inclined to fool around with these stickers, as they really mean business, sometimes up to 5 inches long, needle-sharp, and often divided at the base: the species’ scientific name means “three-spined”. No other tree in our part of the world has thorns quite this size, which makes identification very easy. These are “true” thorns, in that they contain sap-conducting tissues which are continuous with the interior of the tree trunk. (Birders will be familiar with the shrike, or “butcher bird,” which uses these thorns for impaling prey: a grisly lunch.)

Large individual trees may be nearly 80 feet tall, and often with a rounded or flat-topped crown. The bark on an old tree will be dark grey, eventually splitting into ridges. The leaves are compound and somewhat fern-like. Its flowers, which are male and female on the same tree, usually, are greenish and fairly inconspicuous; they appear in late spring. Following the flowers, pale green beans will develop. These beans enlarge dramatically, eventually nearly 2 inches wide and over a foot long. The pods turn a handsome, shiny purple-brown, and almost always curl as they mature. The plump, hard seeds within the pod will be in a line, their linear arrangement easily seen from the outside. Much of the interior of the bean is eventually filled with a moist, fragrant pulp, which is edible. To me, these things are not much worth eating, but that pulp is sort of tasty, sticky, and sweet. Like cocoa paste. (Is there such a thing?) Now, I’ll have to tell you that the common name of this tree includes the word “honey”, not because it’s good for honey production, but because the fruits have that sweet, tasty pulp. At least, that’s my idea.

The beans fall from the branches in the winter, often forming a pile around the base of the tree. These beans are prized by wildlife, including deer; cattle and hogs like to eat them, too. The seeds, once they’ve gone through an animal, will readily sprout, as long as they end up in a sunny place. In the autumn, the foliage turns an attractive, bright yellow.

This species is commonly seen in much of the eastern USA, throughout the Mississippi River valley and into Texas. In the South, it is most often encountered in the piedmont and mountains. It is actually something of a pest sometimes, and has fairly recently been designated as “invasive” in parts of South America and Australia. Here in the USA, these trees are often planted, as they form good windscreens, and are quite hardy, affected by few pests or diseases. They also make a great shade tree for city streets…but then there are those nasty thorns. Well, turns out that a thornless variety is available. Which is good if you want a tree house.

[Answer: “Honey locust,” Gleditsia triacanthos]

John Nelson is the retired curator of the Herbarium at the University of South Carolina, in the Department of Biological Sciences. As a public service, the Herbarium offers free plant identifications. For more information, visit or email

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