The specific origin of the sweetpotato is not known but it is believed to be first grown and cultivated in either Central or South America dating as far back as 6000 BCE. Wikipedia reports that according to one researcher the sweetpotato originated somewhere between the "Yucatán Peninsula of Mexico and the mouth of the Orinoco River in Venezuela." Others propose that the first location of this root vegetable was in Peru. Jennifer Harbster, a Research and Reference Specialist at the Library of Congress, reports in her post "A Sweetpotato History" that: "The earliest cultivation records of the sweet potato date to 750 BCE in Peru...."
So, there is good evidence that the sweetpotato had been around in the South and Central Americas long before the explorer Christopher Columbus brought IT back to Spain in the late 15th Century. One piece that details the origins of the sweetpotato quite extensively is "The Sweetpotato-It's Origins and Primitive Storage Practices" by J.S. Cooley. He states that despite our knowledge of the vegetable in South and Central America "There is no evidence, however, that it was used by the primitive people of Europe, Asia, Africa or Australia. Nor was it known to the ancient civilizations of Egypt, China, Babylon, Persia, India, Greece or Rome." Considering how widely grown the crop is now, especially in China where 80% of the world's supply comes from, it is quite interesting that the vegetable only developed in the American continents.
From the time Christopher Columbus brought it back to Spain on his fourth voyage from the Caribbean , the vegetable quickly spread around Europe due it's favored taste, nourishing qualities and reputation as an aphrodisiac (Sweet Potato Power). Sweetpotatoes most likely made it's way to North America from Europe as we have reports that it was grown in Jamestown, VA as early as 1648. However there is no evidence which lead us to believe that the Native Indians grew the crop. There is a bit of mystery as to how the sweetpotato spread to the Polynesian Islands before the European explorers arrived but one theory has the Islanders traveling all the way to Peru and bringing the crop back around 1000 A.D.