Dioscorea polystachya, Yam C, note the small air bulbils

Dioscorea Polystachya: Yam C

Just like Rambo movies, there is Yam A, Yam B and, yes, a Yam C, the Chinese Wild Yam or the Cinnamon Vine yam, either way we get Yam C, botanical name,  Dioscorea polystachya aka D. oppositifolia (Dye-os-KOH-ree-uh or in Greek thee-oh-skor-REE-uh)   [op-os-i-ti-FOH- lee-uh].  Dioscorea oppositifolia only grows in India, where I presume it is eaten. D. polystachya is the one growing in North America. D. oppositifolia is called by some websites D. batata. Regardless, the accepted name for now for the Chinese Yam is Dioscorea polystachya

In some ways Yam C (Dioscorea polystachya) resembles both Yam A and Yam B (Dioscorea alata, D. bulbifera.) It would almost seem to be a composite. And, yes it has a very edible root and air potatoes. It’s fairly easy to identify, if you know how your three yams differ.  A review:

Yam A, Dioscorea alata, (uh-LAY-tuh) the winged yam, has a very square stem, stem edges can be tinged in purple, it twists lower left to upper right (Z-twist) its leaves are in pairs and more arrow shape than heart-shaped. Its in-the-air bulbils are cylindrical or misshapen lumps, dark brown. The vine can grow to 50 or 60 feet.  Its underground root should be cooked once. Its in-the-air bulbils are considered edible but not too palatable. Yam A is, officially, in three southern states and Puerto Rico.

Yam B, Dioscorea bulbifera, (bul-BIFF-er-ah) the “air potato vine” has a thick round stem, green. It twists lower right to upper left (S-twist)  its leaves are round-shaped heart and singular, alternating. The vine can grow to 80 feet. In-the-air bulbils are round, either tan and smooth, or dark brown with tan pimples. Its underground root needs to be cooked twice, or more and then try carefully. If still bitter discard. Its bulbils are generally not considered edible. Read more about that in the specific article on Yam B. D. bulbifera is in five southern states, officially, and Puerto Rico.

Yam C, Chinese Wild Yam, or Cinnamon Vine, the Dioscorea polystachya. Its deeply lobbed leaves can be round-heart- to  sword-handle shaped to arrow-heart shaped, but to me they resemble a cartoon outline of a rat’s head, with a long nose, large ears. Better still, they resemble the leaves of the Smilax bona nox.  Its leaves

Multiple flower spikes of Yam C, the Chinese Yam

can be opposite on the lower stem, alternating farther up, or arranged in a whorl of three. The vine is round like the D. bulbifera but wiry, it twists lower left to upper right, Z-twist, like the D. alata, to 15 feet. If it blooms its flowers smell of cinnamon. Its leaf margins, petioles, and stems can be tinged reddish purple.  The root should be cooked. Some authors say it can be eaten raw but with so many varieties possible that would not be advised.  Its in-the-air bulbils, often pea size sometimes to golf ball size, are edible and can be cooked up like little potatoes. Each vine produces about 20 bulbils a year. Rats like them, and other small animals. New leaves have a bronze tint which keeps it from being confused with the similar looking Morning Glory. In northern climates D. polystachya is the only local yam.

Roots of Yam C are usually cooked

Yam C, came to the United States as a food and an ornamental crop in the 1800s.  In a 1970 survey it was not reported escaped from cultivation but by 1986 was reported root loose and fancy free. Unlike Yam A and Yam B, Yam C, the D. polystachya, apparently gets around. By 2002 it was reported in 24 states from Vermont south to Florida, west to Illinois and Texas. It’s also been reported in two more since, Wisconsin and Arizona, putting it in 26 states as well as Washington DC, but not Puerto Rico.  In Texas it has become a naturalized “noxious weed.” That title might change if food prices keep rising. In Tennessee it is a Rank-1 Severe Threat Species.  It is becoming an increasing problem in southern Ohio where it is controlled by intense mowing. It is also a favorite ornamental, so your first sighting of Yam C might be inside in the middle of winter in a container.

One-year-old roots weigh about 3 ounces, two-year-old roots, a pound. The root, in good soil, can grow up to three feet long and weight up to five pounds.  Its flavor is between a sweet potato and a regular potato. It is 20% starch, 75% water, 0.1% B1, and has 10 to 15 mgs vitamin C. The most common use is cooked like a potato. The Japanese prefer it raw. However, varieties can differer and I do not recommend you eat it raw. Cook it, or experiment with it raw very carefully.

Yam C, Dioscoria polystachya, is also called the aforementioned D. oppositifolia but I am not convinced they are exactly the same plants which is why I do not recommend the D. polystachya be eaten raw. Dioscorea honors Pedianos Dioscorides, a Greek physician of the first century AD whose book on medicinal herbs Materia Medica was the standard for nearly 2000 years.  Polystachya means many flower spikes. Batata is a Caribbean native word for “potato” and oppositifolia means opposite, as in the leaves. Remember, D. polystachya in North America, D. oppositifolia in India.

Green Deane’s “Itemized” Plant Profile

 HERB BLURB

Externally the raw root has been used to speed up healing because it contains allantoin, a cell proliferant.  Leaf juice can be used to treat snake bites and scorpion stings.

28 Feb. 2006: Abstract: ”A water extract as a viscous solution was obtained from the yam Dioscorea opposita tuber mucilage tororo, and its functional properties were demonstrated. The protein content was about 280 g/mL extract, and the main protein bands with an MW of 33 kDa without 2-mercaptoethanol (2-ME) and 31 kDa with 2-ME were detected by SDS-PAGE. The water extract possessed high antioxidative activity and scavenging activities against superoxide anion and hydroxyl radicals. However, it showed no inhibitory activity against angiotensin I-converting enzyme. The yam tuber contains relatively high contents of vitamins, different micro- and macroelements, enzymes, and dietary fibers. The yam D. opposita tuber will be increasingly regarded as a health-promoting food.”

Dioscorea bulbifera, the infamous Air Potato

The “Cheeky Yam, or Yam on the Lamb

Yam B, Dioscorea bulbifera,  is definitely second best to Yam A, Dioscorea alata. Why is Yam B, the D. bulbifera second best? For two reasons. It requires more work to prepare it to eat, and doesn’t grow as big as D. alata. Let me tell you right now I have dug up one (1) Yam B tuber, but not from lack of trying. Despite decades of looking I’ve only  found one.  Forager emeritus Dick Deuerling, has however. He’s the author of “Florida’s Incredible Wild Edibles.”  Dick was a stickler for taxonomy so when he says he dug up a D. Bulbifera tuber,  not a D. alata tuber, boiled it twice and ate it, I believe him.  I’d ask him to do it again but he died in his 90’s more than a decade ago. I remember that July in 2013 because I had to go to three funerals.

The yam in question, D. bulbifera, ((Dye-os-KOH-ree-uh or in Greek thee-oh-skor-REE-uh))  is the green scourge of Central Florida, ….and South Florida, ….and North Florida…. watch out Georgia here she comes…. It was sent to a researcher in Orlando in 1905 as a possible ornamental and food crop. He reported it would be a dangerous plant to Florida but didn’t kill the plants he experimented with. A little over a century later it now carpets many parts of the state.

That D. bulbifera can be an attractive ornamental is attested by tourists mistakingly taking it home to plant. That it was a potential food crop is debatable. While there may be one species of D. bulbifera there are many varieties. I have noticed, for example, that some have smooth tan round in-the-air bulbils (probably Asian backgound) and others have dark brown bumpy round in-the-air bulbils with tan pimples (probably African background.) What variety was sent to Orlando was not recorded. An Australian version does put on a large root.

D. bulbifera’s underground root is always referred to as toxic but also eaten in some places. How’s that for ambiguous?  And it gets worse, the …. in-the-air bulbils… wrongly called “air potatoes” apparently vary in toxicity, some edible some not. While the bulbils are constantly called toxic by authorities rumor persists they are edible (with special preparation.) In fact I had a visitor from Brazil a couple of years ago while I had some D. bulbifera bulbils (Asian: Smooth and tan) on my desk. He said his mother cooked them all the time. I asked him to ask her how she does it. (Crushes, dries, bakes, leaches then uses.) On the other hand Dick had two friends boil D. bulbifera in-the-air bulbils and had to go to the hospital (Asian or African not known.)  To make matters worse some writers make no linguistic distinction between the above ground in-the-air bulbils and below ground (in the dirt) roots compounding the confusion by calling them both “tubers. ” And technically the underground tubers are not roots but rather “adventurous stem material.”

Yam A, the Alata on our  left with in-the-air bulbils, on the right is Yam B, with in the air-bulbils. No root is shown.

The D. bulbifera has large round ball to heart-shaped leaves and a round stem. It climbs at eye level from your lower right to upper left (called the S-twist) and has in-the-air bulbils that are round, brown and lumpy (African) or round smooth and tan (Asian) hence the nickname “air potato vine.”  And to add to the confusion, Yam A, the Dioscorea alata, (uh-LAT-tuh) has dark brown bulbils as well but they tend to be 1) cylindrical and or 2) very misshapen, neither round or cylindrical, L-shaped, Y-shaped, or a lumpy lump.  D. Bulbifera’s in-the-air bulbils are, to my knowledge, always round regardless of color. D. bulbifera can grow a root about the size of a softball (occasionally to a basket ball,) but apparently does not grow a large root too often if rarely in Florida. That would explain why I have only found one. In fact, I became so frustrated with the D. bulbifera, Yam B,  I put it on the back burner, the way in the back, for over a decade.

Many years later I became a fan of Ray Mears, a British bush crafter. I ordered some of his DVDs and one of his books about wild edibles in England. Unexpectedly, the Dioscorea bulbifera came up. One of Mear’s episodes was about the Aborigines in Australia. They dig up two kinds of yams, one called “long yam” and one called “cheeky yam.” They steam roast them for a couple of hours then eat the “long yam” immediately but not the cheeky yam.” They grate the cheeky yam then leach it in a flowing stream overnight. Then they eat it. No botanical name was given for either yam. But when I was reading his book Mears happens to mention in passing there is one non-edible yam in England. Then he said it is similar to the one the Aborigines eat in Australia,  the D. bulbifera.  Well, as one might expect, that caught my attention. I was beginning to think my friend Dick was the only one who ever found a D. bulbifera root to eat but apparently the Aborigines had found them, too. Alas, we don’t know what varieties.

Researching yams again, this time with the internet, I discovered the “long yams” the Aborigines eat are, Dioscorea transversa. The D. transversa (trans-VER-sa)  like the D. alata, twists when it grows, lower left to upper right, he Z-twist (as does Yam C, the Dioscorea polystachya mistakenly called D. oppositifolia.) The D. bulbifera, however, twists lower right to upper left, the S-twist. By now I was getting the idea that readily edible yams at eye level climb from your lower left to upper right. Z-twist, then behind. The ones that twist the other way, S-twist, need special preparation or are not edible at all. That may seem like a small observation but it took about a dozen years to sort out.

So I do know two things. Dick has eaten the D. Bulbifera undergound root and I have eaten the D. Alta’s underground root. In Dick’s book he says he boiled the root twice to get rid of the bitterness. Then, after peeling, he used it just like cooked potato. In Australia, to remind you, the Aborigines roast it for a couple of hours, grate it, and then leach it overnight in a flowing stream. I know Dick’s method works for Yam B found here in Florida. I don’t know if the Aborigines’ method would work with Yam B’s here.

And what of the bulbils? The bulbils of some D. bulbifera are reported as edible but they require special preparation as mentioned above. Just boiling will not do it. Often their preparation is peeling, sun drying (read long term chemical decay, not short term in an oven) then boiling. Another report is they are soaked then boiled. As third says they are cooked with lye, a method used with some horse chestnuts. A fourth says none of them are edible anyway.

My suspicion is there are different varieties of D. bulbifera and some may be edible in-the-air bulbils. What we do know is that even where they are eaten they are cut open to see if they turn brown quickly. Those that are are not used. And, in some places even after being careful in selecting the Yam B in-the-air bulbils and preparing them the are fed to a dog first to make use.

As a final note of confusion, there is a native Dioscorea in England, the Black Bryony (Dioscorea communis or Tamus communis). It is know as toxic, especially it’s red bulbils/berries. Whether a properly prepared root is edible is unknown. We do know cooking the root changes its chemical makeup, reducing its raphides (calcium oxalate crystals.) The internet also wrongly includes it in the cucumber family.

Green Deane’s “Itemized” Plant Profile

IDENTIFICATION: Dioscorea bulbifera:  ”Air potato vine.’ Large heart-shaped leaves, alternating, stem round,  climbs from lower right to upper left. Bulbils usually tan, round and smooth, Asian, or  round and dark brown with light  dimples, African. Underground root roundish, can be lumpy and distorted when grown in hard soil.

TIME OF YEAR: Fall, September to December. For two months the vine dies back making locating difficult.

ENVIRONMENT: Yams do well in sun or partial shade and prosper with ample rainfall. They require good drainage, and therefore, are often planted on mounds or ridges.

METHOD OF PREPARATION:  Undergound roots, should you find one:  Boil in two changes of water, peel, then slice or mash it, or bake it or chill it and use in a “potato” salad. Make sure it has absolutely no bitterness. I consider the in-the-air bulbils of the D. bulbifera as not edible. If they are it involves considerable process using multiple cooking methods.

Dioscoria alata, yam whose root is most prized

The  Dioscorea Dilemma: Which ones are edible, and what parts?

One wouldn’t think wild yams would be hard to sort out. It only took me about a dozen years.

I’m not talking about anything related to the sweet potato. That’s the Ipomoea family. I’m talking about real yams, in the Dioscorea family. Like many imported plants into warm climates, the Dioscorea (Dye-os-KOH-ree-uh or in Greek thee-oh-skor-REE-uh) have become an invasive weed. And as you know, the motto here is eat the weeds. Let’s see if we can sort them out. There are three escaped yams locally. I call them Yam A, Yam B and Yam C.

The Root of the D. alata, Yam A grown in hard soil

The most common yam in the South is, unfortunately, probably the least edible, Yam B, the Dioscorea bulbifera — B for bulbifera (bul-BIFF-er-ra.)  It was first sent to Orlando in 1905 as a possible ornamental and food crop. The fellow who got the D. bulbifera concluded it was dangerous to Florida but didn’t eradicate while he had the chance. It has since escaped and become a scourge of the countryside. I have not personally proven its edibility. I have a separate article elsewhere on this site called “Yam B: The Bulbifera.”  Yam C is the Chinese Yam or the Cinnamon vine yam. It’s botanical name is Dioscorea polystachya (mistakenly called D. oppositifolia.) It is covered in a different article as well. Yam C: The Chinese. This article is about Yam A, Dioscorea Alata — A for Alata uh-LAY-tuh. It is also called the Winged Yam because its stem is very square.

D. alata, Yam A, under cultivation in soft soil

Yam A, or the winged yam, is also called the “water Yam” the “great yam” the “lesser yam,” and the “purple yam” among others.  It’s not born free anywhere in the world but is a product of cultivation that has escaped into the wild. Researchers think it was an intentional hybridizing of two wild yams by man some 8,000 years ago. So while Yam A, the D. alata, is found in the wild, it is not a wild yam.

Under cultivation, varieties of D. alata  are the most common yam in the world.  It has an underground root that can grow upwards of 7.5 feet long and a 136 pounds (the known record is 180 pounds.)  When cultivated it can grow long and uniform. In hard soil, or in old age, it can be lumpy and malformed. Young roots tend to be solid and straight, older roots tend to branch out. Boiling (or roasting) of the root makes it edible. It got to Africa from Asia around 1,500 B.C. and probably came to the Americas with slaves by the 1700s. By the 1950s D. alata was the most common Yam in the state. The D. bulbifera did not take over for a few more decades.

Above ground differences betwen Yam A, the Alata, and Yam B, the Bulbifera

At first glance Yam A, the D. alta, and Yam B, the D. bulbefera, look quite alike but they have several differences. D. alata’s leaf is an arrow-shaped heart (think arrow-Alata)  D. bulfiera is a ball-shaped heart (think ball-bulifera). The D. alata leaves grow in pairs particularly near the growing end of the vine where as young D. alatas can have one leaf instead of leaves in pairs, the D. bulbifera singly. The D. alata has a large, very square stem with edges tinged in purple, the D. bulbifera has a slight round green stem. The D. alata has bulbils that are dark brown with a variety of shapes, the D. bulbifera has bulbils that are lumpy round and tan (from Asia I think) or round and brown with tan pimples (from Africa I think). Incidentally, D. alata bulbils soaked 4 hours in water germinate three weeks faster than non-soaked bulbils.

The so-called Z-twist goes from our lower left to our upper right at eye-level

The D. alata, when climbing at eye level, twists from your lower left across the surface nearest you to your upper right, the so-called Z-twist. The D. bulbifera twists from your lower right across the surface nearest you to your upper left, the S-twist. I am beginning to think the way of the twist is the first sign of a prime edible yam. Ignore books that say a vine twists clockwise or counter clockwise if they don’t provide you the perspective of the viewer. Depending whether you are looking down or up the same twist can be called clockwise or counter clockwise. If you are looking down at a D. alata it looks to go counter clockwise. If you’re looking up at the D. alata it appears to go clockwise. I have two books that describe its twist in different directions because of the perspective.

Once you learn to tell the differences the D. alata  (as well as Yam C, the Chinese Yam) are fairly easy to spot among their prolific relative, the D. bulbifera. Yam A and Yam C (the Chinese Yam) leaves give them away even at a distance since they grow in pairs. The D. bulbifera has alternating single leaves so from a distance if you see single leaves like a series of steps in a stairs you know it’s not the one you want.  As for availability… along one bike trail I traverse, for one mile all the trees are draped with Yam B. But, there are three patches of Yam A. Yam C is in very isolated pockets.

D. alata’s air bulbils are NOT round and are NOT tan

While the D. Alta has a reputation for being buried very deep that has not been my experience. I usually find the large root within a few inches of the surface. When grown in soft soil the D. alata is long and tubular, when growing in hard soil it will be lumpy and distorted. Old roots can also be lumpy and banched. The largest I have found to date is 8.2 pounds after washing, and that is the norm. Young roots are best used like potatoes, older roots while edible have a different texture, can be fried after boiling or make a good flour. The vine usually puts on one tuber per season but can produce as many as three. Thus the older root can be lumpy but have a younger, well-formed root attached, as the top picture shows.

Sassycrafter and a 30-pound D. alata root

When under cultivation the D. alata is usually left to cure for a week after it is dug up, but that’s not necessary, and it will store for several months. The vine also go into a dormant period. Here in Florida that is about Christmas to St. Patrick’s Day. During that time the vines die back. If you want to dig them up during that time you should mark them earlier in the season. The U.S. Department of Agriculture reports the bulbils of the D. alata are edible cooked but not as palatable as the roots, and my friend, Maribou, has tried them. I, personally, have not gotten around to eating them. It’s on my list of plant things to do.

Dioscorea was named after Pedianos Dioscorides, Greek physician of the first century AD whose book on medicinal herbs Materia Medica, was a standard work until recent times. Alata means winged. Bulbifera means bearing bulbs. Polystachya, many stakes, or blossom spikes.

D. villosa roots are famine food and birth contol, best avoided

For the record, among the semi-edibles yams one might see are: Dioscorea villosa, (vill-LOE-suh) whose roots might be a famine food but with a price. This was the yam from which the first birth control pills were made. There has been some speculation that the Mayans suffered a loss of their maize crop and had to eat D. villosa, causing a fertility drop in their population they could not recover from. (It twines lower right to upper left, the S-twist.)   There are also native Florida yams, but they are rare and have no “bulbils” Dioscorea floridana and Dioscorea quarternata. The native plants are only infrequently seen in north and west Florida hammocks and flood plains. Villosa means shaggy; floridana, Florida; quarternata, four leaves from one place; polystachya many spikes. The word “yam” comes from a west African language and means “something to eat.”

Approximate yam nutrition per 100g: 103 calories; sugars (g)  23; Proteíns (g) 1; Fiber (g) 4; Vitamin B1 (mg) 112; Vitamin B2 (mg) 32; Vitamin C (mg) 17; Salt (mg) 9; Potássium (mg) 816; Cálcium (mg) 17; Phosphorus (mg) 55. It does not have any iron, fat, vitamin A, and no vitamin B3.

Green Deane’s Itemized” Plant Profile

IDENTIFICATION: Dioscorea alata:  Winged Yam. Large arrow-shaped leaves, opposite, stem with four definite sides, edges of the sides often tinged in purple. Stem climbs from lower left to upper right. Bulbils dark brown, round or cylinder, lumpy, mishapen. Underground root similar to a sweet potato in shape when grown is soft soil, lumpy and distorted when grown in hard soil. Can be up to 136 pounds.

TIME OF YEAR:  Fall, September to December. For two months the vine dies back making locating difficult.

ENVIRONMENT: Yams do well in sun or partial shade and prosper with ample rainfall. They require good drainage, and therefore, are often planted on mounds or ridges.

METHOD OF PREPARATION:  Underground roots only: Usually fresh young yam is peeled, cut up and boiled like a potato. Older yams can be pounded into a sticky elastic dough called pounded yam or yam fufu. To make a flour from the D. Alata root slice the underground tubers to a thickness of about quarter inch. Parboil the peeled slices. Dried them in the sun to reduce the moisture content. The dried slices are then ground to flour and sieved to make a uniform texture. Otherwise, the boiled yam can also be used like potatoes.   IF ANY YAM TASTES BITTER, DON’T EAT IT.