Getting to the Root of the Question
First off, let me explain how I arrived at the question, “What the hell is a yam?” I’ve been on a little quest – to find the fabled yam. I started this quest last week, knowing exactly what a yam was… or so I thought.
We’ve had several questions over the past few weeks about the confusion that exists around yams and sweet potatoes. Seems that people are finding contradictory information on the internet, and several people asked us to help them sort things out.
So I thought it would be helpful to put together a simple article with some pictures, to show people how they can tell the difference between a sweet potato and a yam. That couldn’t be too hard, right? They’re two different plants. To be honest, I thought this would be as easy as making two short bulleted lists – voila, problem solved.
That was last week.
I gathered up the facts about sweet potatoes first. That was pretty easy, just like I expected. So I quickly moved on to start gathering up the same facts about yams…
And here I sit, days later – my mind tied into a knot by knotty roots. I set out in search of a few simple facts, and that search led me on a whirlwind tour of world history with more sidebars and tangents than you can imagine.
And so, as I sit here today, I can only ask, “What the hell is a yam?”
Read more: How to Plant Sweet Potatoes
The Mysterious Origins of The Word “Yam”
It’s widely agreed that African Americans started calling sweet potatoes “yams” when soft, orange varieties of sweet potatoes were introduced in the southern United States. Prior to this time, a firm variety of sweet potato had been popular. Supposedly, the new softer sweet potatoes reminded African Americans of the yams they knew from Africa, and so they started calling orange sweet potatoes yams – to differentiate between the old firm sweet potatoes and the new soft sweet potatoes.
That’s a convenient explanation, but on closer inspection it doesn’t make sense, since yams weren’t called yams in most West African languages. They were called isu, ji, viazi vikuu, and other names from African languages.
Some argue that the name “yam” was adapted from Portuguese or Spanish words, and it is possible that the name did travel across the Atlantic on a slave ship – in the mouths of the traders, and not the slaves.
If you check out Webster’s Dictionary, you’ll find that there’s probably some degree of truth to both explanations. They claim the origin of the word “yam” is nyami, which means “to eat” in the Fulani language, which was spoken in West Africa during the slave trade (and today) by people who ate (and whose descendants still eat) yams. The word nyami was adapted to inhame in Portuguese and ñame in Spanish, and then later to igname in French and eventually to yam in American English. So, while yams have been cultivated around the world for ten thousand years, the word “yam” has only been around for the last few hundred years.
However it came into existence, the word “yam” today can mean many things. In a global food market in 2016, saying the word “yam” is about as descriptive as saying the word “root.” There might be 20 different things for sale in that market that are called by the name “yam.” What you get will depend entirely upon whom you ask.
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What the Hell is a Yam? It Depends…
Ask an American for a yam, and you’ll probably get a sweet potato. Ask a New Zealander, and you’ll probably get a root from the wood sorrel known as oca. Ask an African, and you’ll probably get an actual yam.
If you make the mistake of asking a Japanese person, you might get any one of several different plants – a sweet potato, an actual yam, an Okinawan purple yam (which is actually a sweet potato), or a third plant that’s also known as the konjac. As I said before, the word “yam” doesn’t really mean much.
If you ask a Mexican person for a yam, there’s a chance you’ll get jicama, which is also known as yam bean. This plant has another, even more confusing, common name – it is also known as the Chinese potato, even though it is native to America and probably didn’t find its way to China until after the Spanish conquest of Central America. In addition to not being Chinese, jicama is also not a potato. Then again, a sweet potato isn’t really a potato either.
Ask a Pacific Islander for a yam, and you might get taro root. Taro is also known as yam in Southern Spain, and in some Portuguese-speaking countries as well. And the word “taro” could cause you some additional confusion in West Africa, the home of the yam, where taro is commonly known as coco yam.
Finding the Fabled Yam
Of course, there is in fact such a thing as a true yam. But it’s definitely not as easy to pin down as the sweet potato is. All sweet potatoes belong to one species. So while there are hundreds of varieties of sweet potatoes, they are all the same plant – Ipomea batatas.
Not so with the yam. There are at least 8 species of yam that are cultivated for culinary use in the world today. They all belong to the same genus, Dioscorea.
So, right off the bat, you can’t really do a clean comparison of yams versus sweet potatoes. The sweet potato is one plant, and the yam is a big family of related plants.
Meet the Yam Family
And the yam family doesn’t stop with those 8 culinary species – not by a long shot. Those are just the tip of the iceberg.
Yams grow wild all around the world. There are over 600 accepted species in the genus Dioscorea. They predate humans by about 75 million years, and they have a representative on every continent except Antarctica.
There are some native, edible yams that grow wild right here in North America. Fourleaf yam (Dioscorea quaternata), and the wild yam (Dioscorea villosa) are native across the Eastern United States and were used as food sources by the Native Americans there.
Mansplaining Yams and Sweet Potatoes
If you look for information about yams vs sweet potatoes on the internet, you’ll find a million comparisons that say things like “sweet potatoes have smooth skin and yams have rough skin,” and “sweet potatoes are more moist than yams.” Of course, if you’re only holding one or the other, you don’t have anything to compare it against, and this isn’t very much help.
And much of the information that’s out there is targeted at the average American grocery store consumer. So, the overall message you’ll find is something like this, “People in America call sweet potatoes ‘yams.’ Yams are from Africa, and we don’t have yams in America; we only have sweet potatoes.”
That’s sort of right, but it’s sort of wrong too. It assumes that you are someone who would never shop in an ethnic market or a specialty food store; someone who would never forage for wild food; and someone who would never take a random root from the farmers market and plop it in the dirt just to see what happens – and I think I know you better than that.
We’re an American Yam!
We do have yams in America. Actual, true Dioscorea yams. In the age of the internet and the sustainable farming revolution – you better believe that there are yams in America. You want a yam? I can get you a yam by Tuesday…
In addition to the wild yams that are native to America, culinary yams have been grown here, and continue to be grown here – in small volumes by independent growers.
All the way back in 1896, Robert Henderson Price referred to sweet yam (Dioscorea sativa) being grown in Georgia and Florida. He also referred to Chinese yam (Dioscorea polystachya) being imported from France to the US around 1850. That yam had been acquired by the French Consul in Shanghai, while France was trying to find alternative crops to respond to the potato blight in 1848.
In 2009, the USDA reported on 5 species of yams that are considered foreign invasive species in the US – some of which were brought here as food crops.
And in addition to actual yams, there are many other things that might be sold as “yams” that are not truly yams.
More about potato blight: Monocultures
Eating Versus Growing
If you are the “average American grocery store consumer,” then the confusion about yams shouldn’t be a problem for you. You buy your sweet potatoes at the grocery store, cook them, and eat them. Who cares if they’re labeled as yams?
But it’s a little more complicated for the home grower.
In most of North America, making the mistake of planting Dioscorea yams instead of sweet potatoes could cost you your whole harvest. Most of the culinary yams have a growing season that is too long for our climate, and they will freeze before they yield.
Many people enjoy eating their sweet potatoes raw. But most true yams shouldn’t be eaten raw. Some contain toxins, and most contain bitter compounds, so yams are typically soaked or boiled before consumption.
Sweet potatoes also offer more nutrition than yams – so even if you’re in a tropical region where you could grow yams, it probably makes more sense for you to use your precious garden space for sweet potatoes.
So do a little due diligence before you plant, and make sure that you know what you’re putting in the ground. How will you know? The best approach is probably to get your planting material from a source that uses the Latin botanical names for their plants.
In fact, the only person who ever gets a clear answer to the question “What the hell is a yam?” is the botanist.
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Latin, the Universal Language
In the hypothetical global food market we talked about above, there was potentially a lot of confusion about what a yam is. The word “yam” can mean one thing in New Zealand, a different thing in Japan, and yet another thing in Polynesia. It’s confusing all around the world.
But the botanist has no problem. She can ask a Chinese vendor for Dioscorea sativa, and she’ll know that the root she receives is the same plant she gets when she asks a Mexican vendor for Dioscorea sativa. Problem solved.
And it will work just as well for sweet potatoes. Request Ipomea batatas anywhere in the world, and what you get will be a sweet potato.
1: The origin and evolution of sweet potato (Ipomoea batatas Lam.) and its wild relatives through the cytogenetic approaches. http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=016E4C6C53AD973BF8DA3ADC090A514C?doi=10.1.1.617.4992&rep=rep1&type=pdf
2: Library of Congress, What is the difference between sweet potatoes and yams? http://www.loc.gov/rr/scitech/mysteries/sweetpotato.html3: USDA SNAP-Ed Connection, Sweet Potatoes and Yams. https://snaped.fns.usda.gov/nutrition-through-seasons/seasonal-produce/sweet-potatoes-and-yams
4: Wiener, Leo. Africa and the Discovery of America, Volume 1. Innes & Sons 1920. Philadelphia.
5: Price, R. H. Sweet Potato Culture for Profit. Texas Farm and Ranch Publishing Company 1896. Dallas.
6: USDA Plant Profile: Dioscorea. http://plants.usda.gov/core/profile?symbol=DIOSC
7: U.S. Forest Service: Discorea spp. http://www.fs.fed.us/database/feis/plants/vine/diospp/all.html
8: The Congo Cookbook: Yam. http://www.congocookbook.com/staple_dish_recipes/yam.html
9: Wikipedia: Sweet Potato. https://en.wikipedia.org/wiki/Sweet_potato
10: Wikipedia: Yam (vegetable). https://en.wikipedia.org/wiki/Yam_(vegetable)
11: Wikipedia: Taro. https://en.wikipedia.org/wiki/Taro
Very thorough and enjoyable article. Thank you.
Try growing the winged yam. It’s an awesome plant – very easy to grow lots of edible tubers that hang from vines and easy to store. Just don’t confuse it with the air potato, which is toxic, but looks sort of similar!
Popeye ate yams. He would say, “I yam what I yam.” You are what you eat.
Okay? I always thought what you are calling a sweet potato was a yam, and I grew up on a farm in OH. For 75 years I always thought the yam was the sweet potato with many varieties. I know here in CA sweet potato fries are made from those orange things. I thought Californians were there usual crazy selves and mislabeled the yam as a sweet potato. Love the article. And thanks.
Funny! I grew up in the tropics and thought I had figured out how to tell a yam from a sweet potato. The Hawaiian term I was taught for yam is u’a (and it was a very important part of the ancient Hawaiian diet). The Hawaiian name for taro is now generally agreed to be “kalo”, and there are many varieties of kalo to choose from, including the “Chinese taro” an upland kalo, which required a little less water. Their were many Chinese farmers in Hawai’i at one time, and they intermarried with Hawaiian families, resulting in plenty of botanical scrambles, but wonderfully delicious food.
But Michael, wait a second! I thought that the vegetable in the picture you posted as sweet potato would, when baked yield a firm, slightly mealy textured, lightly sweet starchy side dish. And a yam, when baked would produce a saggy, sticky, very sweet but not on my low glycemic diet dessert quality treat. Soooo, the grocery produce shelf that has one basket of orange skinned “sweet potatoes” and a basket of reddish skinned “yams” is likely to be….????
As a gardener, I would love to see botanical terms on produce shelves and gourmet menus. If consumers understood more about food history, they would probably value their small farm and homestead food a great deal more!
Actually those are not the real W. African yams you looking for. They’re discorea sp, the ones rumored to be responsible for high twinning birth rate. Yep! a village in W. Africa (Nigeria) has 4 times the number of twin births more than any where else, hugely due to a diet high in discorea sp. By the way, it’s 600+ species of yams around. No need counting. I like, “I yam what I yam” lol. Yes I’m from W. Africa
Wild yams (Dioscorea) contain a progesterone precursor called diosgenin which may or may not have something to do with the high rate of twins.
I do this with relish. You missed out on the South Sea bit of it. First time I heard of it was in 1963 doing Thor Heyrdahl’s “The Kon-tiki Expedition” (made just after WWII) as a matric setwork. He and four, five others built a balsawood raft to dis/prove the theory of deep sea travel by the peoples living on Easter Island and beyond. (How they got there in the first place.) (The stone faces.) On that voyage one of their staples was yams. Later he also built a ocean going bundled reed boat as you can see in the Egyptian lore, to prove travel between West Africa and South America. Both voyages were successful. The possibility that the endeavours of even earlier peoples are the actual vehicles of the yam’s travels cannot be excluded. Thor’s yams were found in Peru if I remember correctly. Slave trade, my eye!
Wow, you did get yourself into a pickle!
Wrote this without reading others first, but this would connect Sandy and Ode’s comments. The history goes back much further.
I work at an organic market – I was told by a supervisor that Americans saw the yams from another country – we thought they looked like sweet potatoes – when we buy them from another country which calls them yams – we look at them and say “that’s a sweet potato” He said basically, the yam is a big underground root – other countries call it a yam – we will market it as a yam but it is a sweet potato to us. Yes, we put them side by side in the market – so many customers say what is the difference? I say: I was told – The name and where it came from is the difference.
Here (in the Netherlands) we can’t grow both (maybe sweet potatoes indoors). But I can buy both of them. The sweet potato is called ‘zoete aardappel’ (sweet potato in Dutch), or ‘bataat’. We say ‘batata’ or ‘batata dushi’, meaning sweet potato in Papiamento, the language of Curaçao, because my husband is from Curaçao (Netherlands Antilles in the Caribbean).
The ‘real yam’ is mostly called ‘cassave’ or ‘cassava’ here. It is introduced here by Africans.
Absolutely not Inge, cassava (manihot esculanta) is not yam at all. Although a tuber they’re both very different. casavva does not belong to the discorea species of yams.
sorry, the picture looked like cassave to me. If it isn’t, we don’t have yams here.
Lol, that’s funny. It’s a lot of brouhaha about yam isn’t it?
For the humorously inquisitive check out Gloria Gaynor’s ‘I yam wot I yam’ on u tube…
oh the horrors of yam vs. sweet potato! makes me think, have I really ever had a yam 😉 Great info, thanks for your research efforts and for the article 🙂
Appreciate the clarification! We have sat at the dinner table discussing this question and have not been able to come up with a thorough answer. So many places and references to go through on the net. Now I have the answers all in one place! Thanks a million!!
Many, many years ago, I remember seeing two bins in the grocery store—one marked “sweet potatoes” with roots like those pictured in the article, and the other marked “yams” with similar roots which had a more reddish skin and deeper orange flesh. Now I see both varieties interchangeably called either sweet potatoes or yams. While it makes an interesting discussion from a biological and historical perspective, I say if it is nutritious and tastes good and grows or is otherwise available in your area, just eat it!