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A relative of the morning glory, the sweet potato originated in the Andean highlands, and was nurtured by native people for generations. It may have made its way to Polynesia by 700 AD. In 1492 Columbus ate several varieties of sweets offered to him on a Caribbean island and he brought cuttings back to Spain soon thereafter.
A warm weather plant that was never a huge success in Europe, the sweet potato early on was established as a staple crop in the Philippines. By the early 1600’s sweet potatoes were crucial to the eradication of famine in China, and later Japan. The plant transformed culture in Papua New Guinea, remains essential to Maori culture in New Zealand, and became a staple of the American South. It was reportedly being grown in the Virginia Colony by 1648.
Today Japanese people grow many non-sweet, more versatile varieties, and eat them with noodles, as well as in desserts. Americans usually have only three varieties to choose from, all of them fairly sweet. Possibly because enslaved Africans thought sweets resembled the "yams" they were familiar with---yams are tropical plants, and members of a completely different family--they began calling American sweet potatoes "yams." Confusion on this persists to this day.