As most folks in the US prepare for a Thanksgiving meal, or at least eat more Thanksgiving-inspired fall meals, potatoes and sweet potatoes often play a major supporting role in these most delicious victuals. Whether mashed, smashed, baked, candied, or turned into casseroles or pies, these starchy vegetables are stockpiled in grocery stores and markets in the fall for shoppers to turn into those tasty treats.
But sometimes there is confusion lurking in those grocery aisles and even in the minds of unwary shoppers….enter the “yam”. Wander down the canned vegetable aisle and you’ll see canned yams. Are they the same thing as sweet potatoes? And are they related to the standard potato that you usually mash, bake, or fry? I yam going to set the set the record straight.
First things first, sweet potatoes and yams are two totally different species so they are not the same thing. They’re even in different plant families so they aren’t even closely related. And neither of them are related to the regular old potato. So those “canned yams” at the grocery store are mis-named. They are sweet potatoes. Yams are rarely consumed or sold in the US, except usually though markets that sell specifically African/Caribbean foods.
Sweet potatoes are soft when cooked, thin/soft skinned, usually pretty sweet, and usually orange. Though there are some white-fleshed, less sweet varieties available. Native to tropical regions of the Americas sweet potatoes, or Ipomoea batatas, are members of the Convolvulaceae, or bindweed, family and are closely related to morning glories many of which are in the same genus Ipomoea. These sweet veggies are part of the root structure, so they are modified storage roots that store starches and sugars produced by the plant.
Yams, on the other hand, are white with a hard skin like tree bark, and are usually pretty dry when cooked. There are three main species of yams in the Dioscorea genus, which has its own family Discoreacea. Also tropical in nature, three different species were domesticated independently in Africa (D. rotundata), Asia (D. alata), and the Americas (D. trifida). Yams are monocots, meaning they are more closely related to lilies and onions than they are to sweet potatoes. Also, unlike sweet potatoes, the edible portion of a yam is a tuber, which is structure arising from modified stem tissue.
And just to round out the tater trifecta – the humble potato. Sometimes called a white potato or an Irish potato (which are both bad descriptors for them because they come in many different colors, and while they are a staple in Ireland they originate from the Americas), these versatile spuds, Solaunum tuberosum, are members of the Solanaceae family and are closely related to tomatoes, Solanum lycopersicum. Their morphology has similarities to those of the yam, though, as they are tubers arising from the stem vs being a root like sweet potatoes.
So where does all the confusion come from?
There are various theories on how yams and sweet potatoes got caught up in this mash-up, and I don’t pretend to be an expert here. But the most common theory that I’ve seen is that enslaved African people held in the US south called the local sweet potatoes by the names they used for yams, as the sweet potatoes reminded them of the yam that was part of the staple diet in many African countries. The word yam is derived from nyam, nyami, or nyambi, meaning “to taste” or “to eat” in certain African language dialects. Adding to the story, apparently Louisiana sweet potato growers in the 1930s used “yams” as a marketing name for a new orange-fleshed sweet potato cultivar and the name stuck.
One thing I find interesting is that yam was used to describe orange sweet potatoes when the white fleshed ones (which are less common now) would probably more resemble an actual yam, both in appearance and flavor. In fact, in my travels in Rwanda I ate many white fleshed sweet potatoes, as they are now a major staple crop in many African countries. It is also interesting to note that the refugee farmers in our urban farm programs prefer to grow the starchier, less sweet varieties of sweet potatoes, which often complicates things as they can be hard (and expensive) to find.
Whether you cook sweet potatoes or “white” potatoes for your Thanksgiving feast, now you’ll know a little bit about how each of those crops are different…and you’ll at least know that sweet potatoes aren’t yams.