FOR-8 KENTUCKY COFFEETREE:
THE STATE TREE OF KENTUCKY
by Deborah B. Hill and William M. Fountain*
Years ago someone digging through old
law books discovered that Kentucky's legislature had never officially established
a state tree. People considered the tulip poplar to be Kentucky's "official"
state tree as it is in the neighboring states of Tennessee and Illinois.
Politics and state pride being what they are, our state government sought
to differentiate itself from its two neighbors. On February 16, 1976, the
Kentucky coffeetree (Gymnocladus dioica (L.) K. Koch) became the
official state tree of Kentucky when Governor Julian Carroll signed a bill
ending years of controversy on the subject. The Kentucky legislature confirmed
it as the official state tree on March 8th, 1976.
The late Joe Creason, a Louisville
Journal columnist, is credited with initiating and supporting the idea
of making this the state tree. The Kentucky coffeetree is the only state
tree that carries the name of its host state as part of its common name.
The earliest known use of the name
"coffeetree" is found in one of George Washington's diaries from the late
1700s. He was given some seed of this species for planting at Mount Vernon.
The common name coffeetree came about because Native Americans and early
settlers in Kentucky brewed a hot beverage from its roasted seeds.
The name Kentucky coffeetree was promoted
by early land developers who wanted to get settlers out to the "far west"
(which included Kentucky at that time). Coffee, a popular beverage, was
expensive and hard to find away from coastal ports. Land developers advertised
Kentucky as a place where a tree grew with beans that could be roasted
and brewed to make a fine coffee substitute. Although drinkable, the beverage
was no substitute for coffee, and the early settlers quickly dropped it
as soon as the real thing became available.
The literature cites two unusual common
names for this species: "nicker tree" and "chicot." Other common names
include "mahogany" in New York, Maryland and Kentucky, and "butternut"
in Tennessee. There are only two other species in the genus Gymnocladus,
both of which are native to eastern Asia.
The natural range of the Kentucky coffeetree
looks like a broad oval extending from Lake Erie to Oklahoma; it includes
Kentucky on the southeastern side and Minnesota on the northwest. Despite
this broad distribution, the Kentucky coffeetree is one of the most uncommon
trees in the eastern deciduous forest. Some people believe the coffeetree
was introduced into Kentucky by Native Americans. When the European settlers
first came into the area, the coffeetree was found growing in river bottoms
and open woodlands, mostly in limestone areas such as the inner Bluegrass.
Naturally occurring coffeetrees can be found on deep, rich, bottomland
alluvial soils, but when planted as an ornamental, coffeetrees can thrive
over a wide range of soils. The coffeetree often grows in association with
black walnut, honeylocust, yellow-poplar, hackberry, ashes and several
of the hickories.
The coffeetree belongs in Leguminosae,
the pea family. Many members of this family have the capability of fixing
atmospheric nitrogen which enriches the soil in which they grow. However,
like many other woody members of this family, the coffeetree does not have
a nitrogen-fixing bacterium (Rhizobium sp.) on its root system.
It is also free of serious insect or disease problems.
Kentucky coffeetree is a medium to
large tree, usually reaching a height of 75 to 100 feet and a diameter
of 2 ½ feet. Rarely, specimens may be found 120 feet high and 5
½ feet in diameter. The national champion Kentucky coffeetree is
in West Liberty, Kentucky. It has a diameter of 5 ½ feet, a height
of 78 feet and a crown spread of 84 feet.
The genus name, Gymnocladus,
means "naked branch" in Greek, which refers to the network of coarse branches
that typically can be seen without foliage or smaller twigs for about six
months of each year. Without its foliage, the tree takes on a coarse appearance
in winter. Flaky, grayish-brown to dark-brown bark forms on branches as
small as two inches in diameter. These "flakes" have interesting lines
which resemble the lines on a contour map. These characteristics, along
with its persistent seed pods, make the species easy to identify even when
it is dormant.
The Kentucky coffeetree is easily recognized.
Its trunk is short and divides into two to four secondary branches that
are almost parallel to each other. The dark-gray to dark-brown bark is
of medium thickness and has rough projecting ridges. The reddish inner
bark is often visible at the bottom of the "valleys" (fissures) in the
bark. The twigs are stout, greenish-brown and are often coated with a whitish,
crusty film and, occasionally, fine hairs. Inside the twigs is a center
section of pinkish- to reddish-brown pith. Older twigs are marked with
large, orange-colored horizontal openings called lenticels.
The leaves are alternate, bipinnately
(twice) compound (having many leaflets on a single leaf) and can reach
lengths up to 36 inches and widths up to 24 inches, making it one of the
largest leaves found on a native North American woody plant. The subleaflets
are 2 ½ inches long by 1 inch wide and oval with pointed tips and
unequal bases. They have entire margins (no "teeth") and are dark green
above and pale green below.
The species is dioecious, which means
that the tree will be either male or female. The male and female flowers
are greenish-white and occur on separate trees. Coffeetree flowers, which
open in late May to early June after the leaves emerge, smell like roses.
Fruit forms only on female trees, but
a male must be nearby if fruit is to mature and make viable seeds. The
broad, flat, thick pods occur on stout stalks which become obvious in late
summer and persist on the tree until the following spring. These pods are
5 to 10 inches long and 1 ½ to 2 inches broad, giving them the appearance
of a large butter bean pod.
Each seed is the size of a quarter
and is surrounded by a sweet, sticky pulp. The seeds, usually six to nine
in a pod, are dark brown and flat. The seeds contain a toxic alkaloid called
cytisine which is thought to be detoxified by roasting. Cattle have been
reported to die after drinking from pools of water where coffeetree seeds
have been soaking. It is thought that the pioneers used the sticky pulp
around the seed as both medicine and soap.
Culture of the Coffeetree
One can gather ripe pods from trees
in late fall by carefully shaking the branches. It is much faster and easier
to collect ripe pods from the ground the following April. This avoids the
possibility of damaging branches in the process of shaking or striking
them. Small amounts of seed can be extracted from the pods by hand, but
nurseries often use a special macerator (a piece of equipment which softens
the seeds by soaking them) and thresher for seed extraction. After threshing,
the seeds are cleaned in water and the ones that float are discarded.
One hundred pounds of pods usually
yield about 30 pounds of seed. After extraction and cleaning, the seeds
should be placed in cold, dry storage where they can be kept indefinitely.
There are approximately 230 seeds per pound, and 90 to 95% of the seeds
are able to germinate.
Natural germination of coffeetree seed
is often delayed for two or more years because the thick seedcoats do not
break down easily in water. Less than 5% of the seeds usually germinate
without special treatment. The germination time can be shortened by the
immersion of seed in water heated nearly to the boiling point. Another
technique involves soaking the seed in concentrated sulfuric acid for two
to four hours and then washing them thoroughly before planting.
After either of these treatments, the
seed should be soaked in water until swollen. Individual seeds can also
be scraped with a file or emery wheel. Seed treated by these methods can
then be sown and covered with one to two inches of soil. Sow seed in the
spring at the rate of 12 to 20 seeds per linear foot in rows spaced 10
to 12 inches apart. One-year old seedlings can be transplanted to the field,
or transplanting can be delayed if larger stock is desired. Transplanting
in the early spring before leaf growth begins is usually best in Kentucky.
Uses of the Coffeetree
The Kentucky coffeetree reaches merchantable
timber size throughout most of its range and has a tough, durable, often
handsomely-figured wood with many superior properties. The beauty of its
wood has caused it to be compared to the tropical wood ebony. Because of
its rarity in our forests, the logs are often sold in mixture with other
species and lose their identity. It has been used locally for fence posts,
railroad ties, bridge timbers and occasionally for interior trim and furniture.
Its hardness and turnability make it desirable for woodcrafters.
Because of its attractive winter silhouette,
the Kentucky coffeetree is widely planted as an ornamental. Its large leaves
provide almost a tropical setting. It grows rapidly under cultivation and
is highly resistant to insects and disease; even Japanese beetles seldom
feed on it. It is highly resistant to storm damage.
Male trees are recommended for planting
since they do not produce pods that litter lawns and streets. However,
it is the leaves of both types of trees that account for much of the litter
that falls during the late fall and early winter. No cultivars have been
described for the Kentucky coffeetree and, as long as propagation is by
seed, approximately half of every seed lot will be female.
If male trees are more desirable in
the landscape, they can be propagated vegetatively by root cuttings or
grafting. Since the coffeetree is a large tree, care must be taken at the
time of planting to ensure that it will remain clear of power lines, buildings
and other trees.
This species tolerates drought, alkaline soils, pollution, deicing salt,
heat and reflected light, making it a truly tough and resilient, and therefore
highly desirable, landscape and forest tree.
* This publication is based on an earlier version of FOR-8 published
in 1975 by Stanley B.Carpenter.