Kentucky Coffeetree | Glen Arboretum

Kentucky Coffeetree

Gymnocladus dioicus (L.) K. Koc

Description

Kentucky coffeetree is a member of the legume family (Fabaceae) and has numerous additional common names including American coffee bean, American mahogany, niker tree, and chicot tree. ¹ Kentucky coffeetree is a deciduous tree that grows to 100 feet. ¹ Its dark, gray-grown bark is thick and forms plates that curl along the edges. ¹ It has alternate, bipinnately compound leaves that are almost a yard in length. ¹ There are up to 40 leaflets ⁷, each two to three inches long with a smooth margin. ¹ Flowering is “polygamo-dioecious”, ¹ meaning that some plants have bisexual flowers and male flowers while others have bisexual and female flowers on the same plant. Other plants are strictly male or female. ² The flowers are greenish white and are wind-pollinated. Female flowers are in foot-long terminal clusters. ² Mature fruit are brown in color and up to 12 inches long and 2 inches wide. ¹ The fruit contain 4 to 8 very hard, black seeds that are 3/4-inch in diameter.

A close-up of the bright gray bark of a Kentucky Coffeetree, lightly textured with patches of green moss. The bark appears layered, with some sections overlapping as it narrows into a pointed tip

Outer bark of Kentucky coffeetree. BioLib, T. Horova ⁸

Long fans of bright green, ovate leaves stretch outward, their petiole structures visible with sunlight shining down on them. Above them, a large tree casts shade, darkening the background, with glimpses of bright blue sky peeking through the dense canopy.

Leaf of Kentucky coffeetree. BioLib, M. Kesl⁸

A tall, narrow stalk of a Kentucky Coffeetree with a greenish-purple hue. Pale purple flower buds alternate along the stem. Many of the buds have opened into pale green flowers with emerging pistils - others remain closed with pale green tips. Behind the stalk is a cluster of bright green leaves.

Flowers of Kentucky coffeetree. BioLib, M. Kesl ⁸

Two pea pod-shaped seed pods from a Kentucky Coffeetree - one split open down the middle. The outer shell is a deep purple with fine veins running across its surface. Inside, bright yellow flesh holds several glossy black, pea-sized seeds

Fruit and seeds of Kentucky coffeetree. Iowa State University, P. Wyra ⁷

Distribution

The natural distribution of Kentucky coffeetree is from New York to Minnesota, south to Kentucky and Tennessee. It is nowhere abundant. ¹ In Maryland it is listed as S1 (highly state rare) with Garrett County as the only native location. 6 It is naturalized along the Potomac River drainage and in Baltimore and Kent counties. ⁶

Distribution of Kentucky coffeetree. ⁵

Wildlife Importance

Because all parts of the tree are toxic, there is limited wildlife importance. ¹

Economic Importance

The seeds and pods were used as a coffee substitute if they were properly roasted to degrade the toxins. ¹ They do not contain caffeine. ² The hard wood takes on a deep shine and is dark orange or reddish brown ³ leading to its common name of American mahogany. It is used for furniture, cabinets, interior finish and fence posts. ¹

Threats

There are no serious threats or diseases to the plants. ²

Interesting Facts

While a member of the legume family, Kentucky coffeetree is not associated with nitrogen fixation. ¹
The fruit and seeds are poisonous to humans causing stomach pain, nausea, vomiting and coma. ² It contains a toxic alkaloid, cystisine. ¹
The national champion Kentucky coffeetree is in Montgomery County, Maryland. It measures 109 feet tall and 63 inches in diameter. ⁴

References

Contributed by J. Hull

Towson University Glen Arboretum