Thursday, September 13, 2012

Can coffee be made from a Kentucky Coffeetree?

Species name: Gymnocladus dioicus

Common name: Kentucky coffeetree

Location: Ontario

This tree species is marginally native to Ontario; it exists in very limited population numbers in southern Ontario, but has started to gain some popularity amongst gardeners. It should come as no surprise that it was first discovered by European settlers in Kentucky in the United States (where the common name comes from; that's not the only place to which it is native), but the native range extends into Kansas and as far east as Pennsylvania. The northern limit of the range of this species is usually said to be Michigan, although there are relatively old specimens in Ontario so the range probably extended further north into Canada earlier in human history. The status of this species is actually not known in any part of the species range, but it has been suspected to be at the bare minimum a threatened species across all of its range, and likely endangered or critically endangered in some areas. In Ontario it would probably meet the criterion of being endangered; I have only ever seen two Kentucky coffeetrees, and both of those were planted individual trees on Western University campus.

One of the most remarkable features of this species is the incredibly large size of its leaves, and the complexity. It is a member of the bean family or the Fabaceae, so the leaves are by default compound leaves (all members of the bean family have compound leaves). This species has leaves that are referred to as being "twice compound", meaning that the main petiole has side branches off of which grow the leaflets. That phenomenon is illustrated in the last photo: the red arrow points to the swollen base of the petiole where it attaches to the branch, and all of the red lines (compare to the identical photo above it without red lines) are part of one individual compound leaf. The entire length of one compound leaf can be over a meter in length, and almost as wide. They're enormous! With regards to the leaves again, one of the traits that makes this plant one of the least desirable native species is the time of leaf growth and leaf shedding. This is one of the last tree species to grow leaves in this area in the spring, and the first one to shed them in the fall. This isn't indicative of Ontario being the northernmost point in the species' range; this phenomenon even occurs in the most optimal areas for growth. The fruit of these trees are also incredibly messy and require frequent raking to get rid of the seedpods, which is often seen as undesirable by homeowners. The reason why I love this tree in the spring when the leaves first emerge is because of the colour; anyone who knows me personally knows that my favourite colour is pink. When the leaves first emerge from the leaf bud, they are neon pink and fade to green gradually over development.

There is lots of speculation about the origin of the second half of the common name of this plant. There is some evidence of the seeds of this plant being roasted over a fire then ground like coffee and consumed in the same way. Many botanists have their doubts, however, that this is true since the seeds are toxic in large quantities (and this toxicity remains even after boiling and roasting). On the bright side, this toxicity isn't just in the seeds but also in the branches (especially when young). This means it's rarely eaten by herbivores, so is considered very deer-resistant.

Propagation of this plant is incredibly easy. Should you stumble across one of these trees in nature and would like to give it some help in reproduction, you can do your part in helping grow new Kentucky coffeetrees. Collect any mature seeds you find (they will be dry-feeling and incredibly tough) and bring them home to a nail file. Gently file off the surface of the seed until the undercoat starts to show through. You don't need to do this all the way around the seed; even just scraping the surface in one area will be sufficient. Put the seeds into a cup of water for 24 hours, then plant in the ground near where you collected the seeds. Voila! You've just helped in the survival and reproduction of this species.