Even though cooks use the words yams and sweet potatoes interchangeably, they're not the same plant at all.With rare exceptions, every orange-fleshed tuber you see in the U.S. is a sweet potato. Yams and sweet potatoes aren't even botanical kin. Here's what makes these two so distinct:.Yams are starchy root vegetables, closer in flavor to yucca than the sweet potatoes you bake with marshmallows.But in the 1900s sweet potato sellers started promoting red-skinned sweet potatoes as yams.The sweet potato that most Americans would see as standard is a Covington, Beauregard, Garnet, or Jewel variety.Sweet potatoes are fairly similar to white potatoes in terms of calories and carbs.But sweet potatoes have a slight edge on fiber and really shine on vitamins A and C.A single sweet potato provides 90% of the vitamin A you need all day, and 35% of your Vitamin C allowance