Can you tell me the difference between...

Literally and botanically speaking, the two are not related. Both the yam and the sweet potato grow underground and have yellowish-orange flesh, but there the similarity ends. Yams are large, starchy, edible tuberous roots that can grow two to three feet long and weigh as much as 80 pounds. They grow in tropical/subtropical countries and need eight to ten months of warm weather to mature. The two words became entwined in our household vernacular partly through a publicity campaign. Early in this century, sweet-potato promoters attached the word yam to the deep orange, moist-fleshed varieties and left the words sweet potato to the smaller, yellowish, dry-fleshed varieties. Today it is common to find either or both words used in supermarkets, but whichever is used, what’s on sale is the sweet potato.