Tree of the Week: Gymnocladus dioicus (Kentucky coffeetree)

January 26, 2017
Thursday, January 26, 2017 - 12:45pm

By: Natalie Hamilton

Gymnocladus dioicus, also known as the Kentucky coffeetree, is a commonly used shade and ornamental species. It is native throughout the northeast and central United States under USDA plant hardiness zones 3-8. Although it does not produce coffee beans, early settlers of Kentucky gave this tree its name as the beans it produces resemble those of coffee trees.

Kentucky Coffee Tree

 

 

 

 

 

 

 

 

 

The Kentucky coffeetree can reach heights of up to 60-75 feet and has an upright and wide spreading canopy. This tree has a slow to moderate growth rate and displays beautiful bright yellow foliage in the autumn. This species can tolerate a wide range of site conditions and Is free of insect and disease problems. These reasons make it a good street or boulevard shade tree for urban areas. Kentucky coffeetrees have deeply furrowed dark brown bark that appears to peel in strips vertically along the tree. Female trees produce 5-10 inch long pods that contain hard leathery seeds, which are poisonous if ingested raw. This species also produces massive, opposite bi-pinnately compound leaves that are 3 feet by 2 feet long. These unique characteristics make the Kentucky coffeetree stand out as striking and aesthetically pleasing throughout all four seasons.

Kentucky Coffee Tree Characteristics

A cultivar is a variety of a plant that has been selected and bred for desirable traits. Current popular Kentucky coffeetree cultivars include Espresso, Prairie Titan, and Stately Manor. All three of these cultivars are male varieties and therefore do not produce seed pods, which some homeowners find undesirable. If you are interested in planting one of these cultivars in your own yard, know that the availability may be varied. Research may be required to find a nursery near you sells Kentucky coffeetrees.

  • Espresso™ (Gymnocladus dioicus 'Espresso'):  Male cultivar with oval or vase shaped branching spread
  • Prairie Titan™  (Gymnocladus dioicus  ‘J.C McDaniel'):  Male cultivar with a more upright spreading branch habit. Introduced by the University of Illinois.
  • Stately Manor (Gymnocladus dioicus 'Stately Manor'): Male cultivar with a narrow, upright form which may more desireable in compact urban spaces. Introduced by the University of Minnesota.

Germination and The Megafauna Theory

Giant Ground SlothScarification is a process of weakening the coat of a seed. Many seeds, including those of the Kentucky coffee tree, require scarification in order to trigger germination.The Kentucky coffeetrees seed coat is particularly tough and is often soaked in a weak acid in labs to enduce scarification. In nature when a seed pod and seed coat are extremely tough, large animals with strong jaws, such as an elephant or rhinoceros, naturally take care of this. The chewing, ingestion, and passage through the animal's digestive track acomplishes scarification. Today, however, there are no animals within the native range of the Kentucky coffeetree that are capable of doing this. This puzzling phenomenon has made scientists wonder how the Kentucky coffeetree has been able to survive naturally without human intervention. One theory is that the pods of the kentucky coffeetree were once eaten by extinct megafauna. Giant herbivorous mammals, such as the giant ground sloth, once roamed the North American landscape. Scientists believe this overlap in range makes it plausable that these now extinct animals were the ones to scarify and disperse the Kentucky coffeetree's seeds.


All photos and references are used for educational purposes only.

References

  1. Arbor Day Foundation. "Kentucky Coffeetree: Gymnocladus Dioicus." N.p., 2016. Web. 10 Jan. 2017. <http://bit.ly/2id3E6R>.
  2. Department of Horticulture. "Kentucky Coffeetree." University of Kentucky, 1 Nov. 2016. Web. 10 Jan. 2017. <http://bit.ly/2j21Yku>.
  3. ISU Forestry Extension. "Kentucky Coffeetree (Gymnocladus Dioicus)." Trees of Iowa: An Interactive Key. Iowa State University, 17 Aug. 2015. Web. 10 Jan. 2017. <http://bit.ly/2j2fUee>.
  4. Missouri Botanical Garden. "Gymnocladus Dioica." N.p., n.d. Web. 10 Jan. 2017. <http://bit.ly/1tjRC0W>.
  5. The Morton Arboretum. "Kentucky Coffeetree." N.p., n.d. Web. 10 Jan. 2017. <http://bit.ly/2j4IwEo>.
  6. Zaya, David N., and Henry F. Howe. The Anomalous Kentucky Coffeetree: Megafaunal Fruit Sinking to Extinction? (2009): n. pag. Oecologia. U.S. National Library of Medicine. Web. 20 Jan. 2017. <http://bit.ly/2jy0tZv>.

Photos 

  1. Davis, Janet. Gymnocladus dioicus-Kentucky Coffeetree. n.d. Web. 4 Jan. 2017. http://bit.ly/2iQ5YCh
  2. Spencer’s Garden Center. Kentucky Coffee tree :(Gymnocladus Dioicus). n.d. Web. 4 Jan. 2017. http://bit.ly/2jah3kY
  3. Galvan, Jeff. Coffeetree, Kentucky – Trunk. 2016. Web. 4 Jan. 2017. http://bit.ly/2hRMWyF
  4. AQ Nature. Kentucky Coffee-Tree (Gymnocladus dioicus) Leaf Appearance. n.d. Web. Jan 4. 2017. http://bit.ly/2ibupt1
  5. Portrait of the Earth. Seed pods. n.d. Jan 4. 2017. http://bit.ly/2iEz340
  6. Denver Museum of Nature & Science. Giant Ground Sloth. Nov 30. 2010. Web. Jan 4. 2017. http://bit.ly/2iB8xKH