Invasion of the pod plants

by Erik Ault

(Plain Press, October 2022)  Fall officially starts on September 22nd this year, which is also known as the autumnal equinox. The turning of the seasons brings many changes: the foliage will change color, and many trees will produce seeds of great variety. You may know well the acorns of the oak trees or the “helicopters” of the maple trees. But you may have also seen various seed pods and not known which trees propagate in such an unusual way. Though there are many examples in our area, here are three worth noting:

   Black locust tree (robinia pseudoacacia)

   The black locust tree is a hardwood native to the eastern United States. It closely resembles another pod producing tree called the honey locust, but a discernible difference is that the honey locust has long thorns on its trunk whereas the black locust does not. The black locust will produce long, flat seedpods. It is well liked by hummingbirds and bees which use it to produce Acadia honey. But unlike the honey locust, the black locust seeds are toxic. Its hardwood was prized by the Jamestown colonists for timber and by the natives for bows. Notwithstanding its many uses, it is considered an invasive species due to its fast growth and voluminous pod production. It is even illegal to sell this plant in Massachusetts. Nonetheless, we are within its natural habitat, and one can be seen in the back of Monroe Street cemetery.

American sweetgum tree (liquidambar styraciflua)

   You may have seen spiky brown balls along the sidewalk. These are the products of the American sweetgum tree, which is native to the southeastern United States and parts of Central America. It was named this by the famous Swedish naturalist Carl Linneaus due to its sweet-smelling gum — the “liquid amber.” It will produce its spiky balls in the fall which will remain on the tree throughout winter. Despite this, the number of balls each tree yields can present an irritation to pedestrians. Squirrels and some birds do enjoy eating the seeds within the balls but will leave the empty pods behind. For this nuisance though, homeowners can enjoy a beautiful assortment of fall colors for many years.

Kentucky coffee tree (gymnocladus dioicus)

   Standing on the southwest corner of Brevier and W. 18th is a lone Kentucky coffee tree. They are native to this region and are sometimes planted as ornamental trees, but they are rare in the wild. The specimen on Brevier may be the only one in the area. They produce a wide, tough pod whose seeds can be roasted as a substitute for coffee beans. The pod and seeds are poisonous unless sufficiently roasted. The roughness and toxicity of its seed pod contribute to its scarcity. It is conjectured that the pods were eaten, and seeds spread, by now extinct large mammals which could chew and digest the pod unharmed. With the absence of these animals, it is difficult for the plant to disperse its seeds by natural means. However, because it faces so few pests and disease, it is not considered a threatened species.

   Trees reproduce in many ways, and when fall arrives, there will be much to observe. These trees have weathered many changes brought on by human settlement and the cycle of the seasons. And with our knowledge and appreciation, they will remain here as natural anchors for many generations to come.