Archaeologists have unearthed 170,000-year-old whole, charred rhizomes of flowering plants from the genus Hypoxis in a cave in southern Africa. These botanical remains represent the earliest direct evidence for the cooking of plants’ underground storage organs.

“Hypoxis rhizomes are nutritious and carbohydrate-rich with an energy value of approximately 500 kJ/100 g,” said Professor Lyn Wadley from the Wits Evolutionary Studies Institute at the University of the Witwatersrand and colleagues.

“While the rhizomes are edible raw, they are fibrous and have high fracture toughness until they are cooked.”

“They are rich in starch and would have been an ideal staple plant food.”

The researchers found the charred remains of the ancient Hypoxis rhizomes in Border Cave in the Lebombo Mountains.

The rhizomes appear to have been cooked and consumed in the cave by the Middle Stone Age humans.

Border Cave. Image credit: Lucinda Backwell.

“The inhabitants of Border Cave were cooking starchy plants 170,000 years ago,” Professor Wadley said.

“This discovery is much older than earlier reports for cooking similar plants and it provides a fascinating insight into the behavioral practices of early modern humans in southern Africa.”

“Cooking the fiber-rich rhizomes would have made them easier to peel and to digest so more of them could be consumed and the nutritional benefits would be greater,” she said.

Modern Hypoxis rhizomes and their ancient counterparts have similar cellular structures and the same inclusions of microscopic crystal bundles, called raphides. The features are still recognizable even in the charred specimens from Border Cave.

“We compared the botanical features of the modern geophytes and the ancient charred specimens, in order to identify them,” said Dr. Christine Sievers, an archaeologist at the University of the Witwatersrand.

Two charred rhizomes from Border Cave. Scale bars – 2 mm. Image credit: Wadley et al, doi: 10.1126/science.aaz5926.

The Hypoxis rhizomes were mostly recovered from fireplaces and ash dumps rather than from surrounding sediment.

“The Border Cave inhabitants would have dug Hypoxis rhizomes from the hillside near the cave, and carried them back to the cave to cook them in the ashes of fireplaces,” Professor Wadley said.

“The fact that they were brought back to the cave rather than cooked in the field suggests that food was shared at the home base. This suggests that the rhizomes were roasted in ashes and that, in the process, some were lost. While the evidence for cooking is circumstantial, it is nonetheless compelling.”

“The discovery also implies the use of wooden digging sticks to extract the rhizomes from the ground,” said Professor Francesco d’Errico, from CNRS, the Université de Bordeaux, and the University of Bergen.

“One of these tools was found at Border Cave and is directly dated at circa 40,000 years ago.”