Yams and sweet potatoes are often regarded as the same vegetable. Indeed, some grocers interchangeably label both kinds of produce by mistake. However, there is a number of differences between yams and sweet potatoes. While both vegetables can be a nutritious choice, you may actually want one while purchasing the other--unless you know what the differences are.
Although they can somewhat resemble each other, yams and sweet potatoes are actually not even in the same plant family. Yams have one seed leaf and are monocots; sweet potatoes have two seed leaves and are dicots. Yams are more closely related to flowers such as lilies and even grasses, whereas sweet potatoes are more closely related to morning glories. Sweet potatoes originated in North America; yams originated in Africa and Asia.
Appearance is an easy way to tell the difference between yams and sweet potatoes. At as many as seven feet long, yams can grow much bigger than sweet potatoes and are traditionally thicker, too. Yams are black or dark brown in color on the outside and white on the inside, although they can be pinkish or yellowish on the inside as well. The outside of a yam appears almost tree bark-like (although it is still a soft consistency).
There are two primary types of sweet potatoes. Both are smaller than yams. The larger of the two is more oval-shaped and has a light brownish, orange or pinkish skin on the outside. The inside is white, yellowish or pinkish. The other variety may be longer but is thinner as well. It usually appears red or dark pink on the outside with orange or pinkish flesh on the inside. It is these smaller, redder types that are usually labeled "yams" to differentiate them from the other variety of sweet potatoes.
Different Consistency and Taste
Once you get used to the differences, you should be able to identify yams and sweet potatoes correctly by taste alone. Yams are starchier and drier to the touch. They're also less prone to crumbling as soon as they're opened. The larger of the types of sweet potatoes also has a dry consistency (but not as dry as yams) and is quite prone to crumbling. The inside is similar in consistency to a regular potato and tastes only slightly sweeter than a potato. The reddish variety of sweet potatoes is very moist on the inside and very easy to mush once cooked. These types of sweet potatoes are the sweetest variety.
Why There's Confusion
Although there are quite a few differences between yams and sweet potatoes, confusion remains in North America. This is because farmers wanted a word to help explain the differences between the two varieties of sweet potatoes: the large, firm kind and the skinnier, soft kind. Slaves from Africa on North American plantations called soft sweet potatoes "yams" because they seemed somewhat similar to the yam plants they had in Africa, so farmers decided to use the word "yam" to distinguish between the soft and firm sweet potatoes.