Anachronism: a person or thing that is chronologically out of place; especially: one from a former age that is incongruous in the present (Merriam-Webster).
Sometimes, the most exciting plants to find are the misfits- the ones that simply don’t belong in the places they’re found. Last Wednesday while surveying below the bluff near King Farm, Dr. Jon Evans discovered one such misfit: the Kentucky Coffeetree (Gymnocladus dioicus), a new and mysterious addition to the flora of the Domain and of Franklin County. This leguminous tree is most often found in small clumps ranging from New York and Pennsylvania west to Minnesota, south to Oklahoma, and east to Kentucky and western Tennessee, yet it is becoming less and less common throughout its range. Why? Because the Kentucky Coffeetree is an ecological anachronism, a species lost in time.
Before going any further, let us take note of the scientific name of this tree (which tells us a great deal about its life history): Gymnocladus, “naked branch,” refers to the tree’s habit of putting on leaves long after most other trees have leafed out, then being one of the first to drop its leaves in the early fall. For about six months of the year, the Kentucky Coffeetree is ‘naked.’ The species name dioicus indicates that the tree is dioecious, that is, it has distinct male and female individuals and there must be interaction between the two sexes for fertilization to occur (humans are also dioecious).
It would be difficult to identify G. dioicus when it is naked, but we found it fully leafed out (as is typical for July). The foliage (alternate, bipinnately compound, ovate leaves) gave its identity away to Evans, who recalled his first encounters with the tree in his grandmother’s yard. The other tell-tale sign of a coffeetree would be its fruit: large, flat pods 15-20 cm long and 3-5 cm wide, dark reddish-brown in color, ripening in autumn and persisting on the tree until late winter or early spring. Each pod contains four to eight seeds, which, when roasted, produce a suitable coffee substitute (hence the common name, “coffeetree”). A quick search of the leaf litter surrounding our grove of coffeetrees revealed no fallen pods, no seeds. You see, the Kentucky coffeetree is having a tough time with sexual reproduction these days, and it’s not just a temporary rut. The primary way it survives today is through its ability to reproduce clonally by sending out runners. Since we found no evidence of pods (which would indicate sexual reproduction) we have reason to believe that our clump of trees is actually only one genetic individual, stranded from individuals of the opposite sex and thus evolutionarily defunct.
So, why is the Kentucky coffeetree on the decline across its range? Because it’s not going anywhere. The animals that once moved its seeds from place to place are now lost to this world, extinct. There’s no chance that our tiny population will come into contact with other trees of the opposite sex, so there’s no chance of it producing new genetic individuals. It is, essentially, a relic, destined to fade into extinction.
The Kentucky coffeetree isn’t alone; a number of other species (the osage orange, pawpaw, persimmon, and honey locust, to name a few) are also suspected to have coevolved with the extinct group of animals known as the Pleistocene megafauna. A quick glance at the fruit of some of these species should be enough to explain the now-failed relationship: to be desirable to megafauna, you need mega-fruits! Sadly, the hefty herbivores (ground sloths, camelids, horses, mastodons, and more) that once dominated the North American ecosystem went extinct in the Holocene epoch (around 12,000 years ago), leaving stranded the big-fruited trees that depend upon big-mouthed critters for seed dispersal. In the blink of an eye, specialized traits that took millions of years to evolve became obsolete. Though it is uncertain which member of the megafauna once dined on the Kentucky coffeetree’s giant seed pods, it’s clear that the pods have no place in today’s forests. Even if some clever squirrel found a way to open one, the toxic pulp inside would kill it shortly afterward. The tree is a true anachronism, a ghost of the forests of old.
So, if there’s nothing moving the seeds of G. dioicus, what is it doing on the Domain, far from its native range? Herein lays the mystery of this misfit. There are a few possibilities. One, that the trees we saw were actual remnants from the Pleistocene, a vestigial population that was once part of a much larger, contiguous range. The Domain’s population marks the easternmost occurrence of the species in Tennessee, yet it is possible that coffeetrees once grew across the state. The second possibility is that humans (perhaps Native Americans, who drank a brew of the roasted seeds) transported the seeds and intentionally planted them along the benches of the Cumberland Plateau, where a variety of other plants were prehistorically cultivated for food and medicine. Regardless of how it arrived here, we can be sure that the Kentucky coffeetree isn’t going to be doing much travelling in the future, save for the few meters of extension it may achieve through its root system.
Ecological anachronisms like G. dioicus raise some very interesting questions about the past, present, and future of our flora. How can we understand our present assemblage of biodiversity without putting it in the context of the distant past (which is not-so-distant at all in evolutionary terms)? How many North American floral-faunal interactions have been lost or destroyed since European contact? Can species in their demise (like the coffeetree) inform us on how to manage species that are on the brink? How many more misfits are out there on the Domain waiting to be discovered?