Mexican yam, Pachyrhizus erosus, and wild yam, Dioscorea villosa, are unrelated vines. The sweet root of Mexican yam is marketed as “jicama,” and served in tossed salads or separately with olive oil or with lime and chili. Wild yam is native to the eastern half of North American, where native healers used it to treat colic, menstrual cramps and morning sickness. In the lab, diosgenin in wild yam can be converted to the female hormones estrogen and progesterone.
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Mexican Yam – Jicama
Mexican yam is a member of the Fabaceae (pea) family and is a perennial in frost-free areas. Jicama in U.S. supermarkets is imported from Mexico and the Caribbean, but was introduced to Florida and Hawaii. Mexican yam is an introduced crop in Southeast Asia, where it is a widely eaten vegetable. Only the root of Mexican yam can be consumed. All other parts, including stems, leaves, flowers, pods and seeds contain rotenone, a natural pesticide.
Mexican Yam – Legume Crop
Mexican yam is suitable for production on marginal land. Like all legumes, Mexican yam supports nitrogen fixing bacteria on its roots and does not require expensive and potentially environmentally damaging nitrogen fertilizer as a soil amendment. The natural pesticide produced by the plant makes the use of large amounts of expensive, environmentally damaging pesticides unnecessary. Traditionally, Mexican yam was intercropped with corn, which cannot fix nitrogen.
Wild Yam – Habitat
In coastal environments, wild yam’s native habitat is intermittently flooded freshwater marshes and swamps, non-tidal shrub swamps, roadside ditches and the understory of forested wetlands throughout the eastern United States. In mid-continent, wild yam is found vining on shrubs in full sun at the edge of forests that are subject to occasional drought.
Wild Yam – Human Hormone Potential
In the 1960s, hormones for early birth control pills were chemically synthesized in the laboratory from diosgenin, a DHEA-like hormone precursor that occurs naturally in wild yam. This synthesis does not take place in the human body, but based on the supposition that it might be possible, many wild yam products are marketed as supplements for the treatment of menopausal discomforts and painful menstruation. Diosgenin is well documented to reduce harmful cholesterol in studies where animals were deliberately fed high fat diets, but no diosgenin human studies were completed as of 2010.
Sweet Potato Yam
The familiar, commonly consumed sweet potato yam, Ipomoea batatas, is not related to either Mexican yam or wild yam. Ipomoea batatas is a member of the Convolvulaceae (morning glory) family and was anciently cultivated by the Americans of prehistoric Ecuador and Peru.