The terms sweet potato and yam seem to be used interchangeably, but are they the same plant? The answer is no. The sweet potato comes from the Americas (Peru and Ecuador), and the yam is indigenous to Africa and Asia. Unless you are shopping in an international market, chances are what are labeled yams here in the U.S. are really sweet potatoes.
The sweet potato is indigenous to the South American continent. And like its distant cousin the potato, it originally comes from Peru.