Canned yams and fresh yams are often interchangeable in recipes, but many canned yams are candied, or soaked in syrup, and contain more sugar. Many recipes specify whether they require canned or fresh yams.
According to American usage, the term "yam" actually refers to sweet potatoes with moist, orange flesh. True yams are the starchy, edible roots of the Dioscorea genus, which are native to Africa, Asia and other tropical regions. There are over 600 types of yams, 95 percent of which are grown in Africa. To avoid improper classification, the U.S. Department of Agriculture requires that the orange sweet potatoes Americans call "yams" also be labeled "sweet potatoes."