Ralph Brennan's New Orleans Seafood Cookbook isn't afraid of a little controversy. On page 305, the issue of the sweet potato as opposed to the yam is tackled in the introduction to the recipe "Fluffy Sweet-Potato Pie." While yams are common to Africa and South America, the sweet potato ". . . has been a staple of Southern pantries for generations."
At plantanswers.tamu.edu, the two plants are stacked in a side by side comparison of characteristics. The sweet potato had taken root during Neolithic times while the yam entered the scene at around 50,000 BC. Another major difference is in the health benefits each plant provides. While yams are very low in Vitamin A, the orange varieties of sweet potatoes are quite high. In fact, a 3 1/2 ounce serving of baked sweet potato has 8,800 IU of vitamin A with 141 calories, making the root an excellent choice for those watching their weight.
Peggy Trowbridge Filippone at About.com notes that the sweet potato is grown in the Southern United States while yams are primarily cultivated in Africa, parts of Asia and the Caribbean. The first recorded instance of the word "yam" dates to 1676 and is a corruption of African words njam, nyami and djambi meaning "to eat."
Wikipedia.com states that the sweet potato is native to the tropical parts of the Americas and became domesticated about 5,000 years ago. In 2007, Louisiana contributed 15.9% of the American crop of sweet potatoes, making it third in production behind North Carolina and California. Wiki also recounts this story:
The Frenchmen who established the first settlement at Opelousas in 1760 discovered the native Attakapas, Alabama, Choctaw, and Opelousas Indian Tribes eating sweet potatoes. The sweet potato became a favorite food item of the French and Spanish settlers and thus continued a long history of cultivation in Louisiana.The Wikipedia entry for yams comments that the tuber can grow to lengths of 2.5 meters or over 8 feet in length. It began to see cultivation around 8,000 BCE in Africa and Asia. They are particularly valued for their storage in West Africa and New Guinea, up to six months without refrigeration, which is important during the annual food scarcity at the start of the rainy season. Surprisingly, yams of African origin cannot be eaten raw due to the natural substances in the tuber that can cause illness. As well, skin irritation from handling raw yams can occur, although a simple bath of cold water can relieve it.
The Library of Congress explains the confusion over terminology neatly:
Whether a person calls it a yam or a sweet-potato, it makes for delicious food. Fluffy Sweet-Potato Pie is correctly identified as a "delicious comfort food" in Ralph Brennan's New Orleans Seafood Cookbook.
In the United States, firm varieties of sweet potatoes were produced before soft varieties. When soft varieties were first grown commercially, there was a need to differentiate between the two. African slaves had already been calling the ‘soft’ sweet potatoes ‘yams’ because they resembled the yams in Africa. Thus, ‘soft’ sweet potatoes were referred to as ‘yams’ to distinguish them from the ‘firm’ varieties.
Plant Answers: "What is the Difference Between a Sweet Potato and a Yam?"
About.com: "Sweet Potato and Yam Differences" 2008
Wikipedia: "Sweet Potato" 04/29/08
Wikipedia: "Yam (Vegetable)" 04/25/08
Library of Congress: "Question: What is the difference between sweet potatoes and yams?" 03/01/07
photo courtesy of Carl E. Lewis, used under this Creative Commons license