We’re getting a bit of fall color already, especially in the row of smallish honey locusts on Cedar Street between MLK and Sacramento. There are a few of their golden brethren around the corner, too, and more scattered around town and in people’s yards. This is a nice, easy tree if you want light shade and a little drought tolerance. It’s often one of the first trees to go deciduous here, but it seems everyone’s putting the fall colors on early this year.
Gleditsia triacanthos gets its genus name from an 18th century director of the Berlin Botanic Garden, Johann Gottleib Gleditsch, and its species name from its usual habit of bearing triple thorns. The ones planted here—specimens of one of several tame cultivars—have only rudimentary thorns, but you can see some at the joints of the ziggyzag twigs.
Aside from “honey locust” G. triacanthos gets called “black locust” (one of at least two trees with that common name) and thorny locust; three-thorned acacia (it’s not an acacia either.); “honeyshucks”; “sweet locust”; or “Confederate pintree”—because those long thin thorns were supposedly used to pin ragged uniforms together in the late years of the Civil War. It’s native to the eastern United (nevertheless) States, where, in the wild, its thorns can be formidable indeed, reportedly growing a foot long sometimes. They appear in frightening fierce clusters on the trunks, too, not just the twigs.
Amid all that armament is a curious, spectacular seedpod. Look at the Cedar Street trees—especially at the ones that are staying green longest—and you’ll see lots of flat, foot-long pods, extravagantly wavy. These are the reason for the “honey” and “sweet” parts of the English name—and maybe even the “locust,” as a nod to John the Baptist, who lived on locusts and honey, and to the carob tree, called “St. John’s bread.” They’re sweet—they make so much sugar that there have been serious proposals to grow groves of the tree instead of sugarcane.
The wild honey locust is obviously protecting itself against something, and just as obviously trying to attract something. These might be the same things, if Connie Barlow’s thesis in her book The Ghosts of Evolution is correct.
The original distribution of honey locust is not on the upper Midwest prairie, but in the forested East and South. But that big fruit, the spiral pod, is too much of a mouthful for your average rabbit or squirrel; it begs for a big herbivore to eat the sweet pod and disperse the tough seeds inside to places beyond their parents’ reach. But just about the only herbivores big enough, with the right chewing equipment, would be bison and elk, and those have a more northwestern range than honey locust. (Deer are browsers, and like more tender fare.) The seed is incredibly hard to break and scarify, too, and most won’t sprout without being treated very roughly. Early, rather fanciful explanations of the function of the pod—that it rolled away in the wind, breaking open and flinging seeds as it went—stumble on this part of the seeds’ needs.
Barlow proposes that several North American species—honey locust, Osage orange, Kentucky coffetree for example—“remember” the mastodons. Not only mastodons, but horses, too—that line did originate here, but like camels and maned lions, spread to other continents and died out in its hometown. Horses and cattle still find locust pods compellingly tasty; they have sugars, fats, and proteins enough to make them quite nutritious. Other dispersal agents served in the interim, but cattle have spread wild honey locust to a wider range since Europeans came.
Big herbivores often bash tree trunks, or gnaw them to eat sweet inner bark—and that can kill a tree; hence those fierce thorn clusters. The ancestors of that double file of pretty golden trees on Cedar Street may well have equipped themselves to fine-tune the behavior of animal neighbors and commensals who had long vanished from the continent thousands of years before streets—and street trees—were invented.