What is the difference between sweet potatoes and yam?

The yam looks like tree bark, and sweet potato colour is reddish brown.Sweet potatoes have more calories and benefits than yam but it has more vitamin c and beta carotene which converts vitmain A in the body and yams are a bit richer in potassium and manganese.Yam and sweet potatoes taste differently and are totally different plants.Sweet potatoes are referred to as yams to differentiate them from the firm varieties.