Sweet Potatoes and Yams - What's the Difference?
Suppose the whole world thought you and another person who looked similar to you were related, but both of you knew you weren't in the same family? That would be pretty confusing. Here in America, there is a very common family relationship that isn’t what it seems – that’s the sweet potato and the yam – who aren’t related at all, but just about everyone assumes they are. This confusion of two very different species of root vegetables has the United States Department of Agriculture to thank in part for this, since they deliberately labeled one variety of sweet potato (with the orange flesh) as yams just so that they would not be confused with another variety of sweet potato (with the white flesh). Added to this, was the common name of “yam” applied to the orange flesh variety since colonial days in this country, when African American slaves saw them as “yams” that were familiar to them in Africa.
Drawing of a sweet potato -- Art by Jerilee Wei
Yams are monocots, meaning they come from one embryonic seed leaf, whereas sweet potatoes are diocots, meaning they come from two embryonic seed leaves. That would make yams close relatives to lilies or grasses and make sweet potatoes related to the morning glory plant family. There are other differences between yams and sweet potatoes which have to do with:
- the number of parts of the flowers,
- how the petals are arranged, how the roots develop,
- how the veins in the leaves are arranged
Additionally, the sweet potato is actually a herbaceous perennial vine and the ones most familiar to Americans are the over one thousand varieties that originate from Central and South America. The only similarity with a yam is that it is also a herbaceous perennial, but its nine hundred varieties all originate from Africa and parts of Asia.
What does a yam look like? This is a yam.
Orange fleshed sweet potato
In case you are wondering, the sweet potato (not the yam) is related to the common potato but only very distantly.
Additionally, sweet potatoes come in many colors on the outside:
White fleshed sweet potato
- Yellow
- Orange
- Brown
- Purple
- Beige
Finally, be aware that the flesh of this root vegetable can be a rainbow of colors:
- White
- Beige
- Red
- Pink
- Yellow
- Orange
- Purple
And that difference -- is far more important question to be asking about sweet potatoes, because within those sweet potato flesh colors lies a huge difference in wonderful taste of one of the world's most perfectly nutritional food.
Man carrying wild yam out of the jungle.
By comparison, the yam is almost always white fleshed on the inside (although it can also be yellow or pink or even purple in very mature yams. The outside of yams is mostly some form of brown and in a couple of varieties light pink.