Cyperus rotundus, commonly known as purple nutsedge or nutgrass, is considered one of the world’s worst invasive weeds. But new research suggests that prehistoric humans in what is now central Sudan may have gotten an unusual benefit from it.

Stephen Buckley, an archaeological chemist from the University of York in England, analyzed dental calculus — a form of hardened plaque — in fossilized teeth from people who lived thousands of years ago, in the pre-Mesolithic, Neolithic, and Meroitic periods.

In a paper published in the journal PLOS One, Dr. Buckley and his colleagues report that the teeth had remarkably few cavities and high levels of the chemical compounds found in purple nutsedge, suggesting that the plant may have protected against tooth decay.

How might these early humans have used the plant?

“They were eating the tubers, that is, the underground storage organ,” said the senior author of the study, Karen Hardy, of the Autonomous University of Barcelona in Spain. “The purple nutsedge stores its energy and carbohydrates in these underground organs. The main usage by the prehistoric people most surely would have been food.”