Sweet potato (Ipomoea batata) is native to tropical Mexico and Central America and is now among the most cultivated crops worldwide. The transition from gathering to cultivating began in Peru at the end of the Pleistocene ice age. In later farming cultures, sweet potato was grown along with potato, bean, corn, avocado, peanuts and squash. From Peru, sweet potatoes reached eastern Polynesia. Captain James Cook found them in Tahiti and Hawaii in the mid-1700s.
DNA Clues to Natural History
Sweet potatoes are in the Eriospermum subgenus of Ipomoea. DNA studies identify its closest relatives as Ipomoea lacunose, cardatotriloba and umbraticola. Lacunose is a white morning glory native to the eastern United States, California and Mexico. Ubraticola is a pale blue morning glory native to Mexico and Central America. Cordatotriloba is a pink morning glory native to the United States and Mexico. DNA studies of cultivated sweet potatoes found highest genetic diversity in Central America and lowest in Peru-Ecuador, suggesting that Central America is the original population.
Neolithic Cultivation in Peru
Only 10,000 years ago, coastal Peru was dry grassland supporting herds of mastodons, llamas, and horses. By 4,000 years ago, desert expanded along the coast. River valleys became oases for farming cultures. Kitchen waste sweet potatoes were excavated at sites such as Chilca Canyon Tres Ventanas circa 8000 B.C., Punta Grande circa 1900 B.C., and Pampa de las Llamas circa 1800 B.C. Mummy bundles at Paracas Necropolis circa 1400 B.C. include sweet potatoes. At Pachacamac, a late Inca site near Lima circa 1400 A.D., sweet potato remains have starch grains as large as those of modern cultivars.
Researchers do not know how sweet potatoes reached Polynesia. Europeans first assumed shipwrecked Spaniards introduced them to Hawaii in 1528, but that idea is now discredited. Linguists noted similar Peruvian and Polynesian words for sweet potato and assumed prehistoric human contact spread them, but recent research reveals the Spanish introduced the Polynesian term to Peru. Computer modeling indicates that accidental drift from Peru could carry debris or boats to the Marquessas, Tuamotu and the Society Islands in Polynesia.
Europe and North America
Columbus found sweet potatoes among the diet of Caribbean islanders in 1492. He introduced them to Spain and cultivation spread through Europe. The Portuguese carried them into Africa, India and the East Indies. Spanish settlers introduced the sweet potato to Florida and cultivation spread among Native Americans. Genus Ipomoea seeds are common in pre-Columbia Mississippi Valley sites, but were most likely morning glories growing as weeds among corn crops or gathered for hallucinogenic use.
During the late 1500s, sweet potatoes spread from Pacific Islands into Vietnam and then Guangdong Province, China, at Leizhou and the Pearl River Delta. They were directly imported into Fujian by a merchant trading with the Philippines; his family persuaded government officials to encourage their cultivation during the 1574 famine. In the 1600s, the Spanish brought them from the Philippines to Taiwan. In 1606, a minor official brought them from Fujian to Okinawa. From Okinawa, cultivation spread to Japan.