Apios americana, sometimes called the American groundnut, potato bean, hopniss, Indian potato, hodoimo, America-hodoimo, cinnamon vine, or groundnut (not to be confused with other plants in the subfamily Faboideae sometimes known by that name) is a deciduous or evergreen perennial vine that bears edible beans and large edible tubers.
Description The vine of American groundnut can grow to long. It has pinnate leaves long with 5–7 leaflets.
The flowers are usually pink, purple, or red-brown, and are produced in dense racemes in length. The fruit is a legume (pod) long. In botanical terms, the tubers are rhizomatous stems, not roots.
Genetics The species is normally 2n=2x=22, diploid, but both diploid and triploid forms exist. Only diploids are capable of producing seeds; triploids will produce flowers but not seeds. Thus, triploids are entirely dependent on tuber division for propagation whereas diploids can be propagated through both seeds and tubers. Other than seed production, there are no easily identifiable differences between diploids and triploids. Triploids are generally found in the northern part of American groundnut's range whereas diploids predominate in the southern part of the range. Triploids have been identified in Canada (in New Brunswick, Quebec, and Ontario) and the United States (in Connecticut, Vermont, Massachusetts, New York, Pennsylvania, Ohio, New Hampshire, Rhode Island, Wisconsin, and Iowa). A few diploids have been found in the northeastern part of the range, such as along the Black River in Central Ontario. All samples tested in the Southeastern United States have been found to be diploid.
Distribution and habitat The plant's natural range is from southern Canada (including Ontario, Quebec, and New Brunswick) down through Florida and west as far as the border of Colorado.
It grows in marshes (both tidal and non-tidal), bottomland forests, wet thickets, and streambanks.Weakley, A.S. 2020. Flora of the Southeastern United States. Edition of 20 October 2020. University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Ecology The species is a larval host for the Epargyreus clarus. Leafcutting bees from the family Megachilidae are the only pollinator that has been identified, though it has been speculated that the plant is also pollinated by flies.Bruneau A, Anderson GJ (1994) To bee or not to bee?: The pollination biology of Apios americana (Leguminosae). Plant Systematics and Evolution 192:147-149.
Nitrogen fixation American groundnut fixes its own nitrogen, which could be a great advantage in comparison to other roots crops, such as potatoes, true yams, and sweet potatoes. These do not fix their own nitrogen and require large applications of nitrogen fertilizer or cover cropping with nitrogen fixing plants. American groundnut can be nodulated by bacterial strains that are normally found in symbiosis with soybeans or cowpeas.
Research has been done on the potential of the soybean strain Bradyrhizobium japonicum to nodulate American groundnut. It was found that plants nodulated with B. japonicum yielded ~30% better than unnodulated plants if no nitrogen fertilizer was used. It was also determined that nodulated plants partitioned more carbon into non-edible shoots when they were given nitrogen fertilizer, whereas unnodulated plants responded to nitrogen fertilizer with greater tuber yields than nodulated plants. This data suggests that nitrogen fertilization may be required to maximize tuber size and yields in A. americana.
Cultivation
Domestication The American groundnut is generally considered to be an undomesticated crop. In her 1939 description of the Native American use of American groundnut, Gretchen Beardsley states that several historical sources describe the "cultivation" of American groundnut by indigenous peoples. She dismisses the ambiguous term "cultivation" as perhaps referring to the transplantation of tubers near a settlement. She quotes the historical author Waugh on this subject of cultivation: "sometimes planted in suitable locations, though they are not, strictly speaking, cultivated." Subsequent authors on the American groundnut have followed Beardsley's interpretation of "cultivation" when referring to the early use by Indigenous peoples of American groundnut. However, recent evidence suggests that North American indigenous peoples likely intervened significantly as cultivators of the native plants of the region, in a manner similar to contemporary Western permaculture practices. So, from a permacultural perspective, Native Americans may well have "cultivated" the groundnut. Evidence suggests the Shawnee tribe cultivated it with corn and squash in a method known as three sisters gardening. Apios would provide nitrogen for the heavy-feeding squash.
In 1985, Dr. William J. Blackmon, Dr. Berthal D. Reynolds, and their colleagues at Louisiana State University in Baton Rouge, Louisiana, began a program of deliberate de novo domestication of American groundnut. Their primary goal was to develop an American groundnut that can produce a significant yield in a single season. Early trials identified LA85-034 as a promising cultivar, with "elongate tubers of uniform, medium size with light brown skin and little extra rhizomatous material". By 1988, they had collected wild seeds and tubers from 210 plants found in 19 states, although the bulk of their selections came from the state of Louisiana. From these wild materials, and a small number of single crosses, they rigorously selected for plants that met their primary breeding goals of larger tuber size, denser tuber set, single season production, and productivity in untrellised cultivation. The American groundnut domestication program at Louisiana State University continued in various forms until the mid-1990s. Cultivars from this program can still occasionally be found available from small seed companies.
From 1985 to 1994, an Apios breeding program took place that resulted in the collection of over 200 wild accessions. These accessions underwent hybridization and selection, and over 2,200 lines were assessed. Of these lines, only 53 genotypes were kept for further analysis. Three different locations and three different growing conditions—field, pots, and grow-bags—were used. There was significant variation found among almost all of the 20 genotypes in the field growing condition. Inter-node length, plant vigor, and stem diameter during plant growth were positively correlated with the plant yield below ground. There were four distinct genotypic clusters found in this collection of Apios lines. Several genotypes yielded large plants in all locations, maxing up to of subterraneous tuber. This suggests that the plant has a good ability to adapt and grow in a wide variety of locations and conditions. Furthermore, the superior germplasm identified in this project may be suitable as cultivars, and will aid in further development of Apios lines as a crop.
The largest germplasm collection of A. americana cultivars today is found at Iowa State University under the direction of Dr. Steven Cannon. It is maintained there for scholarly and academic use. Research continues at Iowa State on the domestication of American groundnut.
Despite these efforts at domestication, the American groundnut remains largely uncultivated and underused in North America and Europe. There are challenges to breeding and domesticating this plant, as well. There seems to be a partial self-incompatibility with Apios breeding and manual pollinations, resulting in rare seed-sets. Disadvantages in Apios as a crop are its vining habit. The crop has small tuber size for most genotypes. These sizes are typically smaller than ; however, some do average around . The tuber plant is difficult to harvest because of the "beads on a string" arrangement on stolons, which extend for over a meter.
In Japan and South Korea The only place in the world today where American groundnuts are commercially farmed in any significant quantities is in Japan. Before the American groundnut was introduced to Japan, the people on the main island of Honshu and the northern island of Hokkaido were already familiar with a native, wild plant called hodoimo (A. fortunei), which was occasionally eaten as an emergency food. American groundnut was introduced, accidentally or deliberately, to Japan during the Meiji era (1868–1912). One theory is that it was accidentally brought to Japan as a stowaway weed among apple seedlings imported from North America. Another theory is that American groundnut may have been deliberately brought to Japan in the middle of the Meiji period as an ornamental flower.
It has become a culinary specialty of the Aomori Prefecture, where American groundnut agriculture is centered. It has been eaten there for more than one hundred years. Although American groundnut agriculture is primarily identified with agriculture in the Aomori prefecture, it is grown in the nearby prefectures of Akita and Miyagi as well. In addition, it is known to be grown in the southern part of Honshu in the Tottori prefecture. Radioactive testing records following the Fukushima nuclear disaster record cesium testing of American groundnut agricultural products in the central prefecture of Tochigi.
An important part of the spread and popularization of American groundnut consumption in Japan has been the efforts of Dr. Kiyochika Hoshikawa to promote the cultivation of this crop in Japan, and the flurry of scientific articles on the health benefits of eating American groundnut tubers. Japanese websites that sell American groundnut continue to emphasize its health benefits in their marketing efforts. There are reports of American groundnut cultivation in South Korea as well, where it is grown for its nutritional benefits.
Critical agronomic constraints Mechanical harvesting represents the primary barrier to commercial viability. Wild types produce tubers distributed 20-100 cm from the stem along rhizomes at variable depths, while improved 'short-nodded' types concentrate tubers within 30-50 cm but still lack suitable harvest equipment. Modified potato harvesters damage thin-skinned tubers and miss irregularly positioned ones. Hand-harvest labor requirements (40-80 hours/ha) render large-scale production economically unfavorable.
The perennial establishment period requires 2-3 growing seasons for economically viable yields, delaying return on investment compared to annual crops. Vining growth habit necessitates support structures costing $2,000-5,000/ha, though the species fixes atmospheric nitrogen through rhizobial symbiosis, eliminating nitrogen fertilizer requirements. Nitrogen fixation contributes 50-150 kg N/ha annually to soil fertility.
The species exhibits excellent cold hardiness (USDA zones 3-9) and pest resistance with minimal disease pressure. Tubers contain 15-20% protein (dry weight basis)—three times potato content—and all essential amino acids, providing strong nutritional rationale for development despite agronomic challenges.
Louisiana State University breeding program The most comprehensive domestication effort occurred at Louisiana State University from 1985 to 1994 under Dr. William Blackmon and Berthal Reynolds. The program collected over 200 wild accessions and generated more than 2,200 hybrid lines, ultimately preserving 53 elite genotypes. Breeding objectives included increased tuber size, shortened rhizome internodes for clustered production, single-season harvest capability, and reduced trellising dependence.