This Week's Mystery Plant

It's a tree, but it's 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 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 scientific species' 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 grisly shrike, or "butcher bird," which uses these thorns for impaling prey.

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 (male and female on the same tree, usually) are greenish and fairly inconspicuous. Following the flowers, pale green beans will appear. 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 curling as they mature. The plump, hard seeds within the pod will be in a line, their linear arrangment easily seen from the outside. Much of the interior of the bean is eventually filled with a moist, fragrant pulp, which is edible. The beans fall from the branches in the winter, often forming a pile around the base of the tree. These beans are prized by wildlfe, 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.

This species is commonly seen in much of the eastern USA, through the Mississippi River valley and into Texas. In the South, it is most often encountered in the Piedmont and mountains. These trees are commonly 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. (Photo by Linda Lee.)

Photo by Linda Lee