This page is for the millions of families on Thanksgiving bickering over whether there’s a difference between yams and sweet potatoes. There is, and here’s all you really need to know:
- Yams are in the family Dioscoreacea (a monocot, like onion and grass).
- Sweet potato is in the family Convolvulaceae (with morning glory).
- Potato is in the family Solanaceae (with tomatoes and eggplants).
You can see this visually in the graphic below (from the United States Botanic Gardens), which I’ve modified to show the positions of yams, sweet potato (there’s just one cultivated species), and potato (also just one domesticated species).
It is now OK to close this page and go back to cooking. But be sure to make fun of the person who was wrong, especially if that person is not you. If you do the “I’m thankful for…” routine at the dinner table, you might say, “I’m thankful to my biology teachers for being so knowledgeable.”
In case you weren’t part of the cooking today, below is a photograph of three random sweet potatoes that I happen to buy recently (Okinawan purple sweet potato, Beauregard sweet potato, and oriental sweet potato), all shown next to a yellow yam. For a great introduction to sweet potato varieties, read this article by William Woys Weaver.
Unless you are from Africa or Asia (the places where most yam species originate), or shop at H-Mart like I do, chances are good that you’ve never seen a yam in your life, let alone eaten one. The only real exposure Americans have to yams is when females consume progesterone-containing birth control pills — the progesterone is made from a yam saponin (diosgenin). Or at least was … I actually don’t keep up on that, being a guy (anyone know?).
By the way, yams get huge, some too big to fit in your car. I found a newspaper article from Fiji that showed a 304 lbs one (which thus weighed more than all but 3.8 million Americans!). But more recently (2011), an Indian named Mr Raveendran reared a 606 lbs bruiser next to his stationery shop in India. It was organic, too, so that’s probably not the upper limit.
And in areas where yams are common (Africa, Madagascar, Asia, etc.), growing them to impress neighbors is a thing, apparently, and when especially large or amusingly shaped, they make great gifts (I’m not making that up). If you happen to travel to those parts of the world and see crowds carrying them under their arms, you will be instantly reminded of scenes from Invasion of the Body Snatchers where the already-converted carry pods for their still-human loved ones and neighbors. If you are not instantly reminded of those scenes, hurry up and watch that movie.
In case you’re curious, the confusion about yams and sweet potatoes started several hundred years ago, during the slave trade. “Yam” is West African in origin (anyinam means yam; nyami means “to eat”). That “yam” is from a West African language rather than from one of the 1000s of other language elsewhere in Africa or in Asia is a grim reminder that slaves were taken from Western Africa, largely. The first to record the use of the word “yam” were Portuguese slavers. And when Africans arrived in areas planted with sweet potatoes (like on George Washington’s farm) most likely the slaves called them yams, even though they weren’t. As a result, many varieties of sweet potatoes were sometimes labelled yams (e.g., see this book from 1900), especially in the South and especially in regards to sweet potato cultivars that were soft and extra sweet, which may have resembled the “sweet yams” (actual yams, and which were very sweet) that were in cultivation in plantation islands like Jamaica. This caused confusion early on, of course, since most people knew they weren’t really yams. Indeed, a 1921 publication (The Sweet Potato: A Handbook for the Practical Grower) advised that the habit of referring to sweet potatoes yams “best be dropped.” That was sound advice.
Companies have been selling sweet potatoes to Americans for over 200 years, and it’s interesting to consider why they market “yams” over “sweet potatoes”. Labels on boxes of sweet potatoes (or “yams”) used to feature African Americans or soul food menu items (possum, raccoon), revealing (I think) a clear tendency to market to African Americans. Although labels these days are race neutral and possum-free, perhaps choosing “yam” was a way to increase market share among African Americans. A typical African American eats 7.4 lbs of sweet potatoes per year compared to a measly 3 lbs for European Americans (USDA ERS 2002), so a marketing and labeling program that goes after the black market makes good business sense.
The biggest offender for modern-day mislabeling is Louisiana, which has an official policy of calling sweet potatoes “yams,” and seems intent on injecting “Louisiana yam” into the vernacular. So if you are the type who insists that “yam” is a kind of sweet potato, you have been successfully scammed by a Louisiana marketing team. Congratulations! By the way, if you examine a Louisiana shipping box, you’ll find that somewhere on the label is “sweet potatoes” — that’s a USDA requirement. Though Louisiana seems to shrink the font of the actual ingredient so that is it all but invisible. Louisiana has the second highest percentage (32%) African Americans in the United States, after Mississippi. Mississippi, though, seems to market its sweet potatoes as sweet potatoes. As does North Carolina, the largest producer of sweet potatoes in the country.
If you are eating Thanksgiving Dinner with a USDA employee, you might kindly (or otherwise) suggest that they change the law. Allowing shippers to label sweet potatoes as “yams” is the botanical equivalent of marketing prunes as “dates” — a swell way to boost sales of prunes, but also an annoying injustice to reality, especially in a day when everyone is worried about allergies and litigation. And, yes, one can be allergic to sweet potatoes, so if you are in that category and end up dying after eating something mislabeled as a yam, please direct your family to sue Louisiana and the USDA for tens of millions of dollars. That should clear things up real fast.
If you are the produce person at a supermarket, you can do your part by never, ever labeling a sweet potato as a yam. You might even put up a permanent sign that informs customers what a yam is, and that you don’t sell them. Having a sign like that would save you from having to explain it to everyone all the time.
Oh — and then there’s the whole “potato” issue, which came about because the Spanish created the word patata out of batata (the Indigenous name for sweet potato in the Bahama region) and papa (the name for potato in a region of Peru).