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.

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

Leaf of Kentucky coffeetree.  BioLib, M. Kesl⁸

Flowers of Kentucky coffeetree.  BioLib, M. Kesl ⁸

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

1. USDA-NRCS Plant Guide:  Kentucky coffeetree
2. North Carolina Extension:  Gymnocladus dioicus 
3. The Wood Database:  Kentucky coffeetree
4. Maryland Big Trees
5. Gardens Rant:  Pour Me Another Kentucky Coffeetree
6. Maryland Biodiversity Project:  Kentucky coffeetree
7. Iowa State University–Extension and Outreach:  Kentucky coffeetree
8. BioLib:  Gymnocladus dioicus

Contributed by J. Hull

Towson University Glen Arboretum