Dioscorea villosa, Wild Yam - 5 (4)
by Tom Atkinson
Most of us know yams from the produce shelf at the local grocery store, farmers’ market or organic growers. They tend to be solid, relatively dense (when raw), orange in both skin and flesh, and the shape of a warped football. When cooked, the flesh becomes tender, soft even, and succulent. These yams, as we all know, are exotic. They come originally from Papua New Guinea. But did you know that there’s a yam native to eastern North America? I was amazed to learn of its existence, and to discover that it too is edible.
Wild yam (Dioscorea villosa) grows naturally from New England to Minnesota and Ontario, then south to Virginia and Texas. It is found in moist woods, swamps, thickets and hedges. The plant was commonly used throughout its range in North and Central Americas, being favoured by tribes in those regions for pain relief, especially for menstrual cramps. The root also helped to balance hormones (bringing the libido back into balance) and ease the pain of childbirth. The tubers were used for food.
Wild yam is a climbing vine. It climbs by extending its spring shoots up a metre (three feet) or more until it finds something to twine around. Its shoots become a very narrow green stalk (from one to two millimetres or .04-.08 inches in diameter) that can extend upwards over two metres (6.5 feet). The vine will grow up tree branches, tall herbaceous plants (such as goldenrod, Solidago spp.) or whatever else it can find. In the garden, it is an ideal companion for an arbour.
The glory of wild yam is, in fact, the leaves. They are distinctly veined, giving the leaf a quilted or puckered look. The veins commence where leaf petiole meets leaf, and run towards the acuminate tip of the leaf. In fall, the green fades to a clear yellow. Make no mistake, this is a plant grown for its delicate, heart-shaped, shiny foliage.
There is also some hairiness on the underside of the leaves which explains the Latin binomial, villlosa (villous means hairy in English). The Dioscorea part of its botanical name comes from Dioscorides Pedanius (c.40-90 AD), a Greek physician who was born in Anazarbus (today's Turkey). He wrote a text on botany and pharmacology (free from superstition, rare in its day), De Materia Medica ("On Medical Matters"), and served in Nero's armies as botanist.
The leaves of wild yam are wonderful, but the flowers are nothing to write home to mother about. They are pendulous, and consist of small, greenish-yellow flowers along a central stalk. The pollinated flowers form a three-parted seed capsule. (If you hold a seed capsule, and look at it straight on from top or bottom, it is exactly the same as the Mercedes-Benz logo. Mercedes-Benz cars are in good company indeed!) The seeds fall when the parchment-like outer covering is worn away in late autumn or over winter.
Dioscorea species are widely used in modern medicine to manufacture progesterone and other steroid drugs. This plant affords one of the best and fastest cures for bilious colic (hence the other common name, colic-root) and is especially helpful in treating the nausea of pregnant women. It is also taken internally in the treatment of arthritis, irritable bowel syndrome, gastritis, gall bladder complaints and other ailments.
The root is harvested in the autumn and dried for later use, although it should not be stored for longer than one year, since it is likely to lose its medicinal virtues. Caution is advised in the use of this plant. When taken fresh it can cause vomiting and other side effects. Note that edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves.
But are the common edible tuber from New Guinea and eastern North America’s wild yam the only yams in the world? Far from it. A Chinese yam, Dioscorea batatas, is a more vigorous plant, with larger, shinier green leaves than our native. It is hardy in many locales in North America, which is both blessing and curse as introduced plants can escape and trample the native varieties. D. elephantipes, a.k.a. Hottentot’s bread, is a South African plant and an unusual succulent. Its main feature is a large, corky caudex* that grows up to one metre (three feet) in the wild, resembling an elephant's foot (hence the popular name). In Central America, several species of yam are found, including a relatively new one discovered in Costa Rica, Dioscorea natalia, which loves the wet regions of both the Pacific and Caribbean coasts of that country. And new species of wild yams are being discovered (to science) fairly regularly.
I have yet to introduce a friend or fellow naturalist to ioscorea villos a and have a negative, or even neutral, reaction. People are delighted with this simple, yet elegant, vine.
* caudex – thickened, usually underground, base of the stem of many perennial herbaceous plants from which new leaves and flowering stems arise
Growing Wild Yam from Seed
I first encountered wild yam on a walk around what became the North American Native Plant Society nature reserve, the Shining Tree Woods, in autumn 12 years ago. Next spring that vine had many seeds, and I received permission to take a few. (Please note: Ethically, one should always seek permission to collect seed. And no more than 10% of any crop should be taken. We need to let nature work her wonders.)
The seed of wild yam will germinate readily. When you start your plants, you will find that within a few years they will spread by both a more robust root system (which is like five-millimetre or two-tenths of an inch-thick pasta, interconnected versus discrete, and a dark reddish colour) and new shoots from these roots, or by seeds being dispersed by wind and creatures.