What’s the difference between a Yam and a Sweet Potato?

Posted on June 1, 2014

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Yampi (Dioscorea Trifida)

“Yampi” Yam foliage

A guest post by Nate! OMG!

This may be old news for some of you, may be interesting to others, or may be a snooze to still others (so I’ll keep the nerd speak to a minimum).

I’ve recently read a number of blog posts, articles, and heard from folks some breakdowns of the subtle difference between a Yam and a Sweet Potato. There is always a lot of explanation, very few pictures, and a lot of confusion about the description of the tubers, the plants, etc. While I don’t claim expertise or authority, I would like to weigh in on the conversation. Most bits I’ve heard/read on this subject are either confusing or so botanical that my eyes water…so I hope I can find some middle ground. If you don’t feel like reading you can skip to the pictures at the end.

The two vegetables are vastly different. Not like my brother and I are different…more like how a bear and I are different. Shape, smell, color, habits…we both like fish and are mammals… Yams and Sweet Potatoes are both plants and live in the dirt.

The trouble telling the difference is that we are all familiar with Sweet Potatoes, but there is a likely a large part of the US population that has never seen a Yam. I don’t recall seeing a Yam until my mid twenties. This is partly due to the fact that all but a few Yams are extremely intolerant of cold, which to a certain extent isolates them in the warmest parts of of the country. This is also due to the fact Yams are virtually non-existent in american food markets. On the other hand markets purchase Sweet Potatoes by the truck load. To make matters more confusing, in the not so distant past folks decided to start calling Sweet Potatoes “Yams”. Thanks to the name change you can walk in to a grocery store and buy two differently labeled tubers which may not even be different variations of the same species of plant. This is the core of the confusion.

I won’t bother describing the Sweet Potato, we all know what it looks like. But what about the Yam? Yams typically have brown skin, depending on the variety the skin looks a bit like an Idaho potato skin though typically not as smooth. The flesh of most varieties is white or slightly off-white, varying to slightly purple or deep purple. The flesh also feels very slimy. Very slimy. Like you sneezed on your hand slimy. They are LARGE. Some Yam varieties can grow over a hundred pounds. Depending on variety, soil, and age Yams can be knobby/lumpy or long and straight, short and round, but they will almost always grow large and look nothing like a sweet potato.

The most common Yam in the world is the “Winged Yam” (Dioscorea Alata) which also goes by many other names. You can buy one in the Hispanic section of your supermarket (if you have one) next to other exotic looking roots under the heading “Ñame”. If you want a cool purple one find a good Asian market and buy an “Ube”. The Ñame I have found at the grocer are usually about the size of a large coconut, these are typically not the whole yam. Yams cuts and slices heal extremely well and are frequently portioned into smaller chunks for sale (who wants to buy 100 pounds of anything at a time).

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Yam “Ube” climbing

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Sweet Potato crawling (Charlei hates the flashlight in this photo)

I won’t belabor the nerd speak (partly because I’m still pretty new to it) but the botanical difference between Yams and Sweet Potatoes is also stark. Yams belong to the Dioscorea genus, the Sweet Potato belongs to the Ipomoea genus and is more or less a tuberous Morning Glory. Yams are a monocot, meaning they have only one seed leaf (as are onions, ginger, Canna, and others), Sweet Potatoes are a dicot, meaning they have two seed leaves
(as are collard greens, tomatoes, amaranth, and others). Yams are Dioecious (have male and female flowers), Sweet Potatoes are Monoecious (hermaphroditic flowers). Yam vines climb quite high, Sweet Potatoes typically crawl along the ground (Though I’ve seen them work their way up chain link fences). Yams propagate by growing and dropping bulbils that look like tubers growing in the air between the vine’s stem and a leaf. The bulbils vary quite a bit in appearance. Sweet Potato stems root as they crawl along the ground. Yams do not frequently produce seed, Sweet Potato seeds I’ve heard are unpredictable but I have no experience with them. Sweet Potatoes are also so easy to start from roots and stem cuttings that no one bothers with seeds.

Now a pitch for the Yams…

Yams were formerly a commercial crop in the United States, they now grow wild all around us here in Florida. If you are a gardener (in Florida) or are interested in self-sufficiency, low maintenance/high yield crops and you aren’t growing Yams I highly recommend doing so. They are true perennials and require only something to climb. They also grow in the dreadful summer heat and humidity that wreaks havoc on traditional annual root crops. They taste pretty much like a potato, and you can use them same way as a potato. They store well, or you can just leave them in the ground where they use up surprisingly little square footage.

Not to knock Sweet Potatoes. You should grow them too if your climate allows for it. They grow in pathways and tolerate the tromping. You can also eat Sweet Potato leaves, and in Florida greens in the summer are kind of a big deal.

As I stated at the beginning I’m no expert, just a guy with a garden and some very smart friends. The Sweet Potato/Yam confusion has been around long enough that individuals and families have developed their own factors for categorizing Sweet Potatoes as Yams. So I’ll leave you with the words of Levar Burton, “Don’t take my word for it”.

For more information on Yams you can check out Eat the Weeds. You can check out Wikipedia as well, but it might hurt your head and some of the bits you read might seem contradictory.

 

Yam boot

This is no Sweet Potato

Sweet Potato

This is a pretty typical Sweet Potato

More Yams

Three kinds of yams

Sweet Potatos

Sweet Potatoes, also labeled as Yams. This is really the core of the confusion. Marketing.

Purpley Yams

Some Purpley Yams

Yam Pants

This Yam looks like pants…which in my experience seems to be a common configuration for Yams.

photo

Yam Bulbil, these can sometimes also look like pants. It looks large but it’s only about 4 inches long.

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Posted in: botany, food, garden