What is the difference between yams and sweet potatoes?
They are not the same. Here's an answer from the Library of Congress:
Yams, and sweet potatoes are an intrchangeable word in the united states. But they are not exactly the same. sweet potatoes have tapered ends, and are smaller. Yams have rough skin and can grow much larger,sometimes to the size of a football or lager. Tastewise they are very similar and can be substituted for one another.
Likely as not, no. See, 95% of the world's cultivation of yams are grown in West Africa. The remainder originated from Africa and have been developed for the areas they are grown. As trade between Africa and Plymouth Colony, there were no yams at the first Thanksgiving. There were probably sweet potatoes, but sweet potatoes are not yams. No, don't bother arguing. Tomatoes are fruit, strawberries are not a berry and are a vegetable, and…
In the US, what is marketed as 'yams' or 'candied yams' are actually the same thing as sweet potatoes. In Africa and such places you can find real yams, which are whitish pink to purple in color. The only way to tell whether (canned) sweet potatoes or the ones packaged as yams have more sugar is to read the labels of the individual brands.
There are approximately 200 different varieties of yams with flesh colors varying from white to ivory to yellow to purple while their thick skin comes in white, pink or brownish-black. Their shape is long and cylindrical (oftentimes having offshoots referred to as "toes") while their exterior texture is rough and scaly. There is great confusion between yams and sweet potatoes in the United States; most of the vegetables labeled "yams" in the markets are really…
There are sweet potatoes and then there are yams. There is a lot of confusion on which is which. But, I don't want to get into that right now. The short answer is they are about the same. Sweet potatoes have more sugar, but total carbohydrate is very close, if not the same. Sweet potatoes have more beta-carotene, hence, the orange color. Yams are a true root and tend to have more minerals.