Are Thanksgiving Sweet Potatoes and Yams the Same Vegetable?

A Thanksgiving menu says “candied yams,” but the grocery list says sweet potatoes. Did someone change the dish? Probably not. In American food shopping, the two names often point to the same familiar orange-fleshed vegetable. Botanically, however, sweet potatoes and true yams are different plants.

The useful question is what the name means in that particular aisle, package, or family menu. A little plant knowledge helps, but reading beyond the largest word on a label is usually the most practical first step.

Two different plants behind one familiar name

Sweet potato is Ipomoea batatas, a member of the morning glory family, Convolvulaceae. True yams belong to the genus Dioscorea in a separate family, Dioscoreaceae. Royal Botanic Gardens, Kew explicitly distinguishes them, even though “yam” is also used as a common name for sweet potato.

The part sold as a sweet potato is an enlarged storage root. Yams produce underground tubers. Both store resources below ground, which helps explain their broad visual resemblance, but calling them both root vegetables does not make them the same crop.

Nor is a sweet potato simply a sweeter version of the ordinary potato. Kew places the ordinary potato, Solanum tuberosum, in the nightshade family. Similar kitchen roles can hide substantial botanical differences.

What appearance can tell you

Start with skin texture and shape rather than color alone. Iowa State University Extension describes sweet potatoes as having relatively smooth, thin skin and storage roots with tapered ends. True yams are commonly longer and more cylindrical, with rough, scaly skin.

These are clues, not a complete identification system. A large vegetable is not automatically a yam, and an irregular sweet potato remains a sweet potato. If the display is unfamiliar, ask the produce staff for the product name or supplier information rather than deciding from size alone.

Sweet potatoes also come in more colors than the orange Thanksgiving favorite. Mississippi State University Extension’s variety guide lists, among others:

• Beauregard: light rose skin and moderately deep orange flesh.
• Covington: rose skin and orange flesh.
• Murasaki-29: dark purple skin and cream-white flesh.
• O’Henry: cream-colored skin and white flesh.

Those names all identify sweet potatoes. Purple skin does not automatically mean purple flesh, and white flesh does not turn a sweet potato into a true yam.

True yams have their own diversity. The University of Washington’s Elisabeth C. Miller Library identifies purple yam, or ube, as Dioscorea alata, and African white yam as Dioscorea rotundata. “Yam” can therefore refer to several different cultivated species, not one universal vegetable with one appearance.

Why American stores call sweet potatoes “yams”

One commonly repeated explanation concerns the distinction between firmer and softer sweet potato types. Illinois Extension, citing the Library of Congress, describes commercial use of “yam” to distinguish softer sweet potatoes from firmer varieties.

That account helps explain the retail convention; it should not be treated as proof of a single invention date for the name. The important shopping distinction is that “yam” on an American display can describe a sweet potato type rather than a plant in the yam family.

The terminology is documented beyond holiday recipes. The USDA’s National Nutrient Database documentation notes that fresh, canned, and frozen sweet potatoes are sometimes labeled as yams. This is evidence of naming practice, not a reason to assume every product called a yam is a sweet potato.

How to read a Thanksgiving shopping label

Use the whole label and the shopping context together:

1. Read past “yams.” Look for “sweet potatoes” elsewhere on the package, including the ingredient list. If that identifies the vegetable, the larger display name need not send you searching for a different crop.
2. Check the variety when provided. A named sweet potato variety gives more useful information than a generic sign promising “holiday yams.”
3. Ask when identification matters. With loose produce, request clarification. With a catered meal, ask what vegetable the kitchen actually uses.
4. Do not assume specialty-market yams are sweet potatoes. True yams are sold in the United States, including through specialty food stores, as the USDA documentation notes.

At Thanksgiving, “candied yams” may be the familiar name of a sweet potato dish. You can keep the family name on the menu while being precise on the shopping list. The name tells you something about food tradition; the ingredient label tells you what to buy.