WHAT IS THE DIFFERENCE BETWEEN A SWEET POTATO AND A YAM?

It is possible to make an enormous fuss over the difference between sweet potatoes and yams. Botanically speaking, the two vegetables share nothing except for some flowery associations. The yam, a tuber, is a member of the lily family, while the sweet potato is a member of the morning glory family. Yams are usually sweeter, moister, plumper, denser, and a deeper orange color than sweet potatoes -- though not always. The two plants also come from different parts of the world. The yam probably originated in Africa (although it may be the same plant that had been cultivated in Asia since 8000 B.C.); the sweet potato is a New World plant discovered by Columbus (although it may have mysteriously traveled to Polynesia hundreds of years prior to Columbus's first voyage). Slaves in the American South called the sweet potato nyamis because of its similarity to a vegetable of that name that they knew from their homeland. This African word brought the two vegetables together, probably for all eternity, despite botany, archaeology, plant pathology, and the like. And that's probably just as well.

For all practical purposes, it might be more intriguing to think of the yam and the sweet potato as twins separated at birth, growing up with different quirks and twitches but retaining the essential sweet nature that makes them virtually interchangeable from a culinary perspective. Furthermore, the yams generally available in this country are really a variety of sweet potato. (True yams do offer one element missing from sweet potatoes; they contain a compound from which the sex hormone estrogen was first manufactured.)

The value of the sweet potato as a main-course vegetable as well as a dessert has been proven in most cultures and at every American Thanksgiving. The European acceptance of the sweet potato following Columbus's return to Spain was immediate and enthusiastic. The Spanish potato, as it became known, was also soon elevated to the status of aphrodisiac, assuring it an entree to the highest levels of society. Henry VIII had sweet potatoes imported from Spain and made into many types of confections. The distinguished culinary writer and chef Antonin Careme assured the vegetable immortality when he included it in his classic The Art Of French Cooking in the Nineteenth Century. Perhaps less well known is the vegetable's popularity both in China, where it is sun-dried and used for noodle making, and in Japan, where it has been a staple for hundreds of years, especially when typhoons have decimated the rice crop.

But it is the American Thanksgiving that is the true test of the sweet potato's versatility. It is transformed into pies, puddings, and muffins, as well as candied vegetables, biscuits, and even ice cream. The wonder is that, like so many of the foods associated with Thanksgiving, from cranberries and chestnuts to the turkey itself, sweet potatoes are packed away, psychologically speaking, until the next Thanksgiving comes along. Not only can sweet potatoes be substituted in almost any recipe for white potatoes with unexpected and sprightly results, but they make tasty and unusual combinations when saut�ed with garlic and tomatoes, layered in gratins with various types of cheese, or fried in tempura batter and served with dipping sauces.

Credit given to  Louise Fiszer & Jeannette Ferrary
Sally's Place
http://www.sallybernstein.com/food/columns/ferray_fiszer/yams.htm