What makes sweet potato, yam different?

Dear Heloise: What is the difference between a yam and a sweet potato? — Nora P., Stone Mountain, Ga. Sweet potatoes usually are sweeter than yams. Yams are starchier. Sweet potatoes contain calcium, iron, protein, beta carotene, sodium, vitamin A and more sugar and water than yams. Yams have more fiber, potassium and vitamins C, B-6 and E than sweet potatoes, but also more fats and carbs. Sweet potatoes are believed to have come from Central or South America, while yams are believed to have originated in Africa and Asia. West Africa is still where the majority of yams are grown. Sweet potatoes are readily available in most grocery stores, while yams usually are more available in international markets. There are two main varieties of sweet potatoes in the U.S. and Canada. One is pink-skinned and orange on the inside; the other is golden-skinned and white on the inside. With yams, the outer skins usually are dark-brown or light-pink. The insides can be pink, white, yellow or purple. — Heloise Dear Heloise: You had a marinade for lamb that my husband really liked. It not only improved the flavor of the meat, it helped reduce the cooking odor in the house. Sadly, I lost it when we down-sized to an ew home. Would you reprint that recipe? — Nancy H., Kinston, N.C. Nancy, yes. The lamb marinade also is great for beef and veal. So, here is your recipe: 1 cup dry white wine or red wine 1/4cup cider vinegar 1 cup salad oil 2 teaspoons salt 1/2 teaspoon black pepper ⅛ teaspoon dry tarragon 1 bay leaf, crushed into small pieces 1/2 teaspoon thyme or marjoram 1 large clove garlic, finely chopped Combine all ingredients in a medium bowl and use as you would a commercial marinade. Remember, you can only use a marinade once. This prevents cross-contamination of bacteria, which in turn can cause illness. — Heloise