Centenary College Arboretum: Kentucky Coffee-Tree (Gymnocladus dioica)

Friday, August 30, 2024

Kentucky Coffee-Tree (Gymnocladus dioica)

In our contemporary situation of free and easy global trade, yearly consumption of coffee beans amounts to almost 25 billion pounds. You can get a cup almost anywhere, anytime. But since Coffea arabica can only be grown in a relatively few environments, war or trade embargoes can easily cut off coffee supplies to most places on earth. Due to this problem and the recognized benefits of the drink, coffee substitutes have often been sought and utilized. Today we'll showcase the arboretum's Kentucky coffee-tree (Gymnocladus dioica).

It isn't native to Louisiana. The map below shows that the plant is really a Midwestern fellow, with its distribution dipping down into the southeast.

This map shows the current distribution according to the USDA-NRCS. The Kentucky coffee-tree (Gymnocladus dioica) does not typically grow in Louisiana. Since it can be found in central Arkansas, this species certainly deserves representation in the Centenary arboretum.

There are two Kentucky coffee-trees growing in the arboretum. There is a big one, and right next to its trunk, there is a little one, which is clearly waiting for one of the surrounding trees to die so that it might have a chance to grow. These two trees do not have an official entry in the arboretum catalogue. They are mentioned elsewhere, in regards to other plants, but their specific planting history is missing. In an entry for spiderwort, the Kentucky coffee-tree is mentioned: "Another large clump [of spiderwort] with the seedling Gymnocladus dioica, below iris bed in west floodplain, planted 1999." A Kentucky coffee-tree seedling was growing in a pot with spiderwort, and they were planted together in the west floodplain in 1999. So, the Kentucky coffee-tree is at minimum 25 years old. According to the Iowa University Agriculture and Natural Resources Extension, the tree should be sexually mature and fruit-bearing once aged 20-30 years. Interestingly, this tree came to our attention this week because we found an unusual seed pod in the leaf litter.

This seedpod was found in the west floodplain under the Kentucky coffee-tree. Since the species is dioecious, that means our tree is female, but where is the male? How was it fertilized? The pod was cracked open and one seed was removed. It was in poor condition, so it was discarded.

Two more fruits were found. One is significantly larger.

The larger pod has one seed.

It's a large seed, mearsuing approximately one inch across.

The seed is round and dark brown.

As with the Yapuon holly (Ilex vomitoria), the Native American Indians of the Southeastern Woodlands are reputed to have consumed a tea made from the seeds of Gymnocladus dioica. The paucity of consumer goods in colonial times, being a major issues for homesteaders and travelers, there has been interest in this tree's seed since at least the late 18th century. Some people employed the Kentucky Coffee-Tree as a coffee-substitute up to and possibly during the American Civil War, when a Union blockade cut off the Confederate States of America from international trade. It was greatly inferior to the alternatives, such as chicory and scorched barley, as an uncaffeinated coffee substitute. Experiments performed by John P. Spaeth and John W. Thieret in the earlier 2000s showed that although potable, this drink was generally squalid. While true coffee addicts would consider such a product little better than a criminal act, a hot herbal beverage is better than nothing on cold days and long nights. Let's now check out the specimen itself.

The Kentucky coffee-tree is pictured center. It grows in a heavily shaded floodplain. All lower branches have been removed, so it will easily be missed as "just another tree" unless one is looking for it.

The wish-bone shape of this tree is no doubt a response to growing in heavily-shaded conditions. This tree is clearly adaptable.

It was planted near a Pinus taeda, an on-site native. From its first planting in the arboretum, the Kentucky coffee-tree has had to compete for sunlight, leaning away from the looming pine tree. Alas, it's good to have friends, even if you have to share your place in the sun. These trees have known each other for a long time.

The photos below were taken during the winter months. They allow us a less-cluttered view of the landscape.

Clumps of spiderwort (Tradescantia ohiensis) grow at the base of the Kentucky coffee-tree trunk. Spiderwort was planted at the same time as the coffee-tree.