New evidence confirms that the sunflower was domesticated in Mexico more than 4,600 years ago, researchers say, contrary to the widely held belief that it was converted into a food crop only in the Mississippi Valley.
"Given all the available data, the best explanation is that the sunflower was domesticated twice," said archaeologist David L. Lentz of the University of Cincinnati.
The sunflower has been an important food crop in the Americas, both for its high fat content and its oil. It also played a role in many religious rites.
Lentz reported seven years ago that he and his colleagues had discovered a 4,600-year-old sunflower seed and achene, the sunflower fruit containing the seeds, at San Andres in Tabasco state on Mexico's Gulf Coast.
But critics, including Bruce Smith of the Smithsonian Museum of Natural History, argued that the remains were not really sunflower. Smith also said that genetic analysis indicates that sunflowers from Mexico and the United States have the same origin.
Many experts think that Spanish conquistadors were responsible for bringing domesticated sunflowers to Mexico from the north.
A new discovery from a site called Cueva del Gallo in the central state of Morelos confirms the earlier find, Lentz and his colleagues reported Monday in the Proceedings of the National Academy of Sciences. They discovered three well-preserved achenes that they say are indisputably sunflowers and that date from around 300 BC, 1,800 years before the Spaniards' arrival.
"The Cueva del Gallo shells are in excellent condition and have unmistakable sunflower traits, removing all doubt about the pre-Columbian presence of domesticated sunflower in Mexico," said coauthor Mary D. Pohl of Florida State University.
The large size of the achenes identifies them clearly as domesticated varieties. The achenes are about 30% larger than those of domesticated sunflowers from Mississippi Valley sites of the same period, suggesting an independent origin, Lentz said.
The team also interviewed indigenous people in different parts of Mexico where sunflowers are grown today. Eleven of the 14 groups had unique words for "sunflower" that bore no relationship to either the Spanish word for the plant or the names used farther north.