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Sweet Potatoes vs. Yams

As people gather for meals during the fall holiday season, there are bound to be disagreements, such as the age-old debate: Are those sweet potatoes, or yams?

Kelly Murray Young, an assistant agent of horticulture for the UA Cooperative Extension in Maricopa County, can settle the debate: Sweet potatoes and yams are not the same thing. They aren't related. Not even close.

"The way we talk about plants is different from how we talk about groceries," Murray Young said.

"A green bean is actually a fruit. But in a grocery store, we don't think of green beans that way," she said. "When we think about how living things are related to one another – how humans are so different from jellyfish, for example – we come to these different divisions. Sweet potatoes are as different from yams as humans are from snakes."

It's all in the classification.

While both come from groups of flowering plants, yams, which are starchier than sweet potatoes, are in a classification of plants referred to as “monocots” while sweet potatoes are classified as “dicots”, Murray Young explained. In fact, the more brightly orange and sweeter sweet potato is in the morning glory family while yams are more closely related to agave, she also said.

The rising theory about why there exists widespread confusion about sweet potatoes and yams draws its source from the days of slavery in the U.S.

"What is understood is that African slaves in the U.S. thought sweet potatoes were yams, because they look very similar. That's where the confusion got picked up," she said.

Also, yams are very hard to find in the U.S., save the occasional farmers' market or specialty store, said Murray Young, who, along with her colleagues in Phoenix, hold public workshops to teach people how to grow sweet potatoes at home and in community gardens.

While yams have long growing seasons and tend not to grow well in Arizona, sweet potatoes have a shorter season and thrive. Their edible leaves, which can be used for salads, can be harvested all summer long, with the root ready to eat in the fall, Murray Young said, adding that sweet potatoes generally need only 90 to 100 days of growth before they can be harvested.

"It's hard to find greens that grow through the summer months, and people are becoming more and more interested in eating local and fresh foods," Murray Young said. "And people all over the world eat sweet potato leaves; it is an important part of the diet for people."

For those who generally cook sweet potatoes during the fall season, Murray Young urges people to go for the fresh roots.

"Try sweet potatoes fresh out of the grocery store instead of a can," she advised. "Try different styles. You can add your own sugar to bring it to the sweetness you like, or try it without butter to see how delicious it is." 

And check out this Mashed Sweet Potatoes and Turnips recipe from the American Institute for Cancer Research:

You'll need:

  • One medium sweet potato at about 3/4 pound that is peeled and cut into 2-inch pieces.
  • One medium turnip, peeled and cut into 2-inch pieces.
  • 1 table spoon of canola oil
  • 1/2 cup of diced onion
  • 1/4 cup of finely diced Italian parsley
  • 1/4 cup shredded reduced-fat Swiss or Gruyére cheese
  • Salt and freshly ground black pepper, to taste

To prepare the dish, put a steamer in a large pot with about two cups of water, sitting the potatoes and turnips on the steamer. Bring the water to a boil, steaming the vegetables for 15 minutes, or until they are tender. While the vegetables are boiling, sauté the onion and parsley over medium heat in the canola oil. This should take about five minutes. Then, put the cooked potatoes and turnips in a large bowl and mash them with a folk. Stir in the onion, parsley and oil, then season the lot as you like with salt and pepper. Finally, lightly coat a baking dish with oil spray and add potato mixture. Be sure to press down evenly. Top that off with your cheese, broil it for no more than three minutes, or until the cheese begins to bubble and brown. And there you have it – enough for four servings. 

Curious about the nutritional chart? The dish, per serving, carries 121 calories, 4 grams of total fat, 4 grams of protein and 3 grams of fiber. 

Contact: Kelly Murray Young at 602-827-8219 or kyoung@arizona.edu.