Gymnocladus dioicus (L.) K. Koch

Kentucky Coffee Tree

Gymnocladus_dioicus_plant.jpg
STATS

Native
CC = 6
CW = 5
MOC = 56

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Family - Fabaceae/Caesalpinioideae

Habit - Trees 10-20 m tall, usually incompletely dioecious, sometimes colonial from root suckers.

Gymnocladus_dioicus_canopy.jpg View of canopy.

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Stems - Bark unarmed, shallowly grooved, silvery gray, often reddish-tinged, developing longitudinal scaly ridges and becoming dark gray on older trunks, the branches not producing short shoots but the leaves sometimes tending to be clustered toward the branch tips, the twigs stout, the winter buds inconspicuous and strongly sunken into the twig. Root nodules absent.

Gymnocladus_dioicus_bark.jpg Bark.

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Gymnocladus_dioicus_twig.jpg Twig and leaf petioles.

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Leaves - Petiole 10-20 cm long, glabrous. Blades 30-90 cm long, 2 times pinnately compound, with 4-7 pairs of pinnae, each with 4-6 pairs of alternate leaflets, the lowermost pair of pinnae sometimes replaced with a pair of large leaflets. Stipules inconspicuous and scalelike, shed early. Leaflets 2-9 cm long, 1.5-5.0 cm wide, ovate to broadly elliptic, rounded to angled at the base, short-tapered or tapered to a sharply pointed tip, the margins entire and inconspicuously short-hairy, the upper surface glabrous, the undersurface finely hairy.

Gymnocladus_dioicus_leaf.jpg Single leaf (partial).

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Gymnocladus_dioicus_leaflets1.jpg Leaflets adaxial.

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Gymnocladus_dioicus_leaflet2.jpg Leaflet abaxial.

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Inflorescences - Racemes or narrow panicles, mostly appearing terminal, 14-20 cm long, ascending to spreading, sometimes entirely staminate or pistillate on a single tree, but often with some inflorescences having mixed imperfect and perfect flowers. Flower stalks 10-35 mm long.

Gymnocladus_dioicus_inflorescence.jpg Inflorescence.

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Gymnocladus_dioicus_inflorescence2.jpg Inflorescence detail.

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Flowers - Perigynous, actinomorphic, fragrant. Hypanthium 8-12 mm long, tubular to narrowly funnelform, densely hairy. Calyces of 5 sepals, these subequal, 4-7 mm long, narrowly oblong-elliptic, sharply pointed at the tip, moderately to densely hairy, not closing the flower in bud. Petals 5, 4-10 mm long, 1.5-2.5 mm wide, greenish white, densely woolly. Stamens 10, unequal in 2 alternating long and short series, the filaments not fused, hairy at the base, the anthers 1.2-1.6 mm long, attached toward the midpoint. Style short, relatively straight, the stigma oblique.

Gymnocladus_dioicus_flower.jpg Flower (4-parted).

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Gymnocladus_dioicus_hypanthium.jpg Hypanthium.

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Gymnocladus_dioicus_corolla.jpg Corolla.

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Fruits - Legumes 9-15 cm long, 2-5 cm wide, 1.0-1.5 cm thick, more or less oblong, straight or slightly curved, rounded or short-angled at the base and sometimes with a short stalk to 0.5 cm long, abruptly short-tapered to a usually sharply pointed tip, 1-4-seeded, the valves velvety when young, becoming woody and glabrous, persistent into the winter, the valves dehiscing with age along the ventral suture, seeds with a stout attachment and embedded in a green, jellylike pulp. Seeds 15-20 mm in diameter, ovate to circular, somewhat flattened but turgid, dark reddish brown, hard, shiny.

Gymnocladus_dioicus_fruit1.jpg Fruit.

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Gymnocladus_dioicus_fruit2.jpg Fruit interior.

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Flowering - May - June.

Habitat - Forests, streambanks, bases of bluffs.

Origin - Native to the U.S.

Lookalikes - Juglans nigra, Ailanthus altissima, Robinia pseudoacacia, and others are trees with pinnately compound leaves.

Other info. - This tree is found in scattered locations throughout most of Missouri and the U.S. Midwest. The inflorescences are distinctive but usually not seen, as they are normally high up. The leaves are more easily observed in the canopy overhead, and can be distinguished from the listed lookalikes by virtue of being doubly pinnate. The unique fruits are often found littering the ground beneath the tree, and these serve as unambiguous indication of the nearby presence of the species. The large pods normally contain only a few seeds, which are embedded in a gelatinous pulp.

Conventional lore holds that the seeds were roasted and ground as a coffee substitute by early settlers. An interesting 2004 paper from J.P.Spaeth and J.W.Thieret of Northern Kentucky University described experiments designed to replicate the beverage, as well as to rate its palatability using a tasting panel of 20 volunteers (SIDA, Contributions to Botany Vol. 21, No. 1, 2004, pp. 345-356). The authors drily noted of the tasting that "no one claimed to enjoy the taste or experience," and that the plant "poses no serious threat to Maxwell House or Starbucks."

Native Americans also used the roasted seeds as food. Unroasted pods and seeds are toxic, probably due to poorly characterized glycosides and saponins. It seems likely that raw seeds could also cause dental injury because they are as hard as rocks. Many references state that the seeds contain cytisine (not to be confused with cytosine), an alkaloid which has been investigated for smoking cessation and could contribute to toxicity. However, the source of this claim is obscure, and at least one modern study has failed to detect the alkaloid in the seeds.

Photographs taken at various parts along the Katy Trail in Warren and St. Charles Counties, 3/29/2010, 3/9/2012, 7/25/2019, 2/16/2020, and 5/23/2020 (SRTurner).