Nightshades are plants that belong to a group called solanaceae. While potatoes are considered nightshades, yams are not. Some doctors believe that there is connection between eating nightshades and pain and inflammation conditions like arthritis.
A yam is a starchy root that belongs to the Dioscorea genus. Originating in the Caribbean, yams have brown, scaly skin with white meat. The name came from the African name "nyami."
Since yams do not belong to the nightshade family, they do not contain the toxic substance solanine, which can interfere with a brain enzyme and cause problems with muscle function.
Yams are not the same thing as sweet potatoes, although people use the name interchangeably. Sweet potatoes, which also do not belong to the nightshade family, have soft, orange flesh and a sweet flavor.