Sweet potatoes are lower in calories and higher in beta-carotene and vitamin C than yams. Yams have slightly more potassium and manganese. They both contain decent amounts of B vitamins. Both have great health benefits. However, yams and sweet potatoes are very different and come from opposite parts of the world.  Sweet potatoes come from South America and are a member of the morning glory family.  Originating from Africa and a part of the lily family are our Yams. They are both tuber vegetables and have similar shapes. Over 600 varieties of yams are known, and 95% of these are still grown in Africa.  Yams are darker, almost black, and have a rough texture.  Yams are also mushier (due to their higher water content) and have higher sugar contents.  However, yams do not taste sweeter even with more sugar.   Yams, true yams, can be hard to find, unless you frequent international or ethnic food stores.  They are long like sweet potatoes, but do not taper at the ends.