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AUTHOR

David Trinklein
University of Missouri
Division of Plant Sciences
(573) 882-9631
trinkleind@missouri.edu

The Incredible Groundnut

David Trinklein
University of Missouri
(573) 882-9631
trinkleind@missouri.edu

Published: January 10, 2020

root vegetable

James St. John

When the first Pilgrims arrived at Plymouth Rock in 1620, they found Native Americans consuming a plant growing in the wild they referred to by various names including hopniss. Today we refer to the plant as groundnut. History records that, because of its widespread abundance, this plant helped many European immigrants survive the rigors of harsh colonial winters. It is likely groundnut frequently allowed early colonists to avoid starvation. Today, it is virtually unknown to most Americans.

Although peanut (Arachis hypogaea) at times carries the common name of groundnut, the plant which is the subject of this article is Apios Americana, or the American groundnut. Like peanut, it belongs to the Fabaceae plant family and, as such, is a nitrogen-fixing legume.

American groundnut is native to a vast area of North America stretching from southern Canada southward to Florida and westward to Colorado. In contrast, peanut (native to Bolivia) did not arrive in North American until the 18th century.

A perennial vine that can grow up to 18 feet in length in the wild, groundnut is a remarkable plant in that nearly every part of it is edible. Of greatest value as a food source are its seeds which can be eaten like peas, and its tubers. The latter are swellings that occur along underground stolons, not unlike beads on a necklace. They normally range in size from about two to four ounces. In addition to starch, tubers of groundnut contain about three times the amount of protein as Irish potato. Additionally, they are rich sources of calcium and iron.

Referring to groundnut tubers, Henry David Thoreau once wrote, "With a little salt a hungry man could make a very palatable meal on them." They can be boiled, fried or baked and, by many, are reported to have somewhat of a nut-like flavor. Their texture is like a soggy potato.

Recently, human nutritionists have become increasingly aware of the medicinal value of groundnut. In one study, hypertensive rats displayed a 10% decrease in blood pressure when five percent of their diet was comprised of groundnut tubers. Additionally, a reduction in cholesterol and triglycerides was noted. Subsequent research revealed that tubers of groundnut contain compounds known as isoflavones (e.g. genistein) that have a variety of health benefits including anti-carcinogenic action against breast, colon and prostate cancer. In other studies, the consumption of flowers of groundnut was shown to lower blood glucose levels in diabetic mice.

Attempts to improve American groundnut have met with only guarded success, due to the complex genetic makeup of the species. Both diploid and triploid forms of the plant exist in the wild, with only the diploid forms able to bear viable seeds. Louisiana State University maintained a groundnut breeding program in the late 1980s which was aimed at improving tuber size. Although not officially released by LSU, several superior varieties resulted from their work, some of which still are available. Today, Iowa State University maintains the largest germplasm collection of this species for research and other scholarly use.

Groundnut remains an obscure food source, most often obtained in the United States through wildcrafting. The tubers require two years to mature which is too long for it to be an economically viable crop. Additionally, its vining nature makes it challenging to grow on a large scale. Japan is the only country that grows the plant commercially as a food crop, placing great emphasis on its health benefits. In recent years, South Korea also has begun producing tubers of the plant for the health food market.

For venturesome gardeners who would like to attempt to produce groundnut, it is best to start with whole tubers instead of seeds. The latter tend to be genetically heterozygous which results in uneven plant stands and irregular yields. Tubers are available online from various sources such as Norton Naturals (www.nortonnaturals.com), Sand Mountain Herbs (www.sandmountainherbs.com) and (even) eBay (www.ebay.com).

Plant tubers in a well-drained soil in (at our latitude) a partial shade exposure. Plants are very tolerant of soil pH but adequate moisture is important. Given plants are slow to establish, tubers should not be harvested until the second (or third) year following planting.

Waiting until the top of the plant is exposed to freezing temperatures tends to cause the tubers of groundnut to taste sweeter. Harvesting is accomplished by digging a section of the plant and pulling tubers from the stolons on which they are borne. Since groundnut is a perennial, it is important not to harvest all the tubers so that the plant will return the following growing season. Harvested tubers have a storage life of several months under cool, dry conditions.

It is important to note that tubers of American groundnut should not be consumed raw because of toxic protease inhibitors they contain. The latter are denatured by cooking, thus, rendered them harmless. However, care should be exercised when consuming even cooked tubers for the first time. A small percentage of people who eat them report symptoms of gastric distress ranging from cramping to extreme abdominal pain along with vomiting and diarrhea. Start with small portions and increase from there, if gastric symptoms do not develop.

red and white flower

Judy Gallaghe

In addition to the above, American groundnut has potential in the landscape as an ornamental because of its attractive flowers. It bears pinnately compound leaves on vines that can reach eight to ten feet or more in length. Its pinkish-brown flowers are borne on conical racemes three to five inches long. In addition to being edible, its pea-like flowers emit a fragrance likened by some to that of cinnamon.

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REVISED: January 10, 2020