Fall Color Series: Gymnocladus dioicus
Hello again, Devil Mountain bloggers!
This week, we’re going to take a look at another deciduous tree, Gymnocladus dioicus and specifically the named cultivar ‘Espresso,’ developed by J. Frank Schmidt Son & Co.
Commonly recognized as the Kentucky Coffeetree, this species derives its botanical name from the word gumnos meaning naked and klados meaning branch, referring to the fact that this tree drops its foliage and remains leafless for many months. The specific epithet dioicus means dioecious, having separate male and female forms.
– Jean-Pol GRANDMONT [CC BY-SA 3.0] –
This species is native to the Eastern United States, can you guess which state? Drumroll please… Kentucky! Much of this tree’s native distribution falls within state boundaries of Kentucky where the state’s first settlers roasted and brewed the fruits and seeds as a coffee substitute – this is another source of inspiration for the tree’s common name!
As the specific epithet hints, there are both male and female forms of this species – Gymnocladus dioicus ‘Espresso’ being a seedless male cultivar. Female forms produce exceptionally large seed pods that are unique as they require scarification to induce germination. While many plant seeds germinate readily in normally ideal environmental conditions, many also fail to germinate readily because of physical or physiological dormancy. Physical dormancy is caused by the structure of the seed – hard seed coats for example, which is the case with our Gymnocladus – and these husks can be worn or weakened to allow gases and water to permeate and induce germination. Physiological dormancy is caused by the presence of germination inhibitors, which may be removed by storing seeds at extremely hot or cold temperatures or in highly humid environments (but that’s another post for another day…).
– Dimìtar Nàydenov [CC BY-SA 3.0] –
The type of scarification that Gymnocladus requires to spread is usually provided by megafauna (mega – large & fauna – animals) consuming plant parts, and in turn seeds. Chewing up and digesting seeds accomplishes a necessary breach in their husks, and allows them to germinate after they exit the animal. This factor makes the presence of Gymnocladus especially exceptional in the States, as we do not have any naturally established species of megafauna quite like those of Africa and Asia. Without megafauna populations it is a mystery as to how this tree was able to establish the wide habitat distribution it has today without human intervention. Some hypothesize that this is due to historic populations of now-extinct giant ground sloths that once roamed the North American landscape.
– Jean-Pol GRANDMONT [CC BY-SA 3.0] –
Typically found in low woods, bluff bases, or along streams in the natural landscape, this tree may grow to reach 60 – 80’ and sometimes but (rarely over) 100’ tall. In the cultivated landscape they are often selected as a shade tree or ornamental specimen, and they will reach about 40 – 50’ tall and 30’ wide. As the tree matures it begins to form an irregular, open oval to vase-shaped crown of large, tropical-looking pinnate leaves up to 3’ long. Each leaf is divided into 3 – 7 pairs of pinnae, which are further divided into individual 1 – 3” leaflets. Late spring brings a show of greenish white flowers, male flowers in 4” long clusters and female flowers in 12” highly fragrant clusters. Pollination of female flowers leads to the production of previously mentioned seed pods. Leaflets present a cool blue green during summertime, and shift to dramatic soft golds and yellows in fall before dropping to the ground. Because this tree’s leaves emerge late and fall early, the tree is bare most of the year and shows off its deeply furrowed brownish gray bark.
Best grown in rich and well-drained soils but is highly tolerant to poorer quality soils and drought, this urban-tolerant tree is adaptable to a wide range of habitats and landscapes. Full sun is the ideal condition for this tree, allow for at least 6 hours of direct unfiltered light each day. There are no serious pest or disease problems, however, leaves and seed pods from female trees may cause unwanted litter. Single plantings make a dramatic specimen, or this tree works well planted in mass as a shady grove.
We offer both Gymnocladus dioicus and the Gymnocladus dioicus ‘Espresso’ cultivar. For the straight species, we offer 15g, and for the ‘Espresso’ we offer 15g and 24” boxes.
Companion plants for Gymnocladus: Sesleria (Moor Grass), Leucophyllum (Texas Sage), Salvia (Salvia), Syringa (Syringa), Lonicera (Honeysuckle)
“Gymnocladus dioica.” Missouri Botanical Garden. https://bit.ly/2PkjFdH.
Hamilton, Natalie. “Tree of the Week: Gymnocladus dioicus.” University of Minnesota – UFore Nursery & Lab. https://bit.ly/2RokZ1T.
“Kentucky Coffeetree – Gymnocladus dioicus.” Arbor Day Foundation. https://bit.ly/36dfYgW.
“Kentucky Coffeetree.” University of Kentucky. https://bit.ly/38djyJK.
“Propagation.” Encyclopedia Brittanica. https://bit.ly/2RqGy1K.