Not much difference but everywhere ive read they are indeed different.
Yam or sweet potato, what in the world is it? Many people use these terms interchangeably both in conversation and in cooking, but they are really two different vegetables.
Sweet Potatoes
Popular in the American South, these yellow or orange tubers are elongated with ends that taper to a point and are of two dominant types. The paler-skinned sweet potato has a thin, light yellow skin with pale yellow flesh which is not sweet and has a dry, crumbly texture similar to a white baking potato. The darker-skinned variety (which is most often called "yam" in error) has a thicker, dark orange to reddish skin with a vivid orange, sweet flesh and a moist texture.
Current popular sweet potato varieties include Goldrush, Georgia Red, Centennial, Puerto Rico, New Jersey, and Velvet.
Yams
The true yam is the tuber of a tropical vine (Dioscorea batatas) and is not even distantly related to the sweet potato.
Slowly becoming more common in US markets, the yam is a popular vegetable in Latin American and Caribbean markets, with over 150 varieties available worldwide.
Generally sweeter than than the sweet potato, this tuber can grow over seven feet in length.
The word yam comes from African words njam, nyami, or djambi, meaning "to eat," and was first recorded in America in 1676.
The yam tuber has a brown or black skin which resembles the bark of a tree and off-white, purple or red flesh, depending on the variety. They are at home growing in tropical climates, primarily in South America, Africa, and the Caribbean.
Yams contain more natural sugar than sweet potatoes and have a higher moisture content. They are also marketed by their Spanish names, boniato and ñame.
