Evidence of plant tubers, similar in shape to a carrot, being cooked in the fire by ancient humans has been discovered in a cave on the KwaZulu-Natal/Eswatini border.

“The inhabitants of the Border Cave in the Lebombo Mountains … were cooking starchy plants 170,000 years ago,” said Professor Lyn Wadley, a scientist from the University of the Witwatersrand’s Evolutionary Studies Institute.

The underground food plants were uncovered during excavations at Border Cave, where a team has been digging since 2015. They 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,” said Wadley.

During the excavation, Wadley and Wits scientist Dr Christine Sievers identified 55 charred, whole rhizomes as Hypoxis, commonly called the Yellow Star flower.

The team said the most likely of the species growing in KwaZulu-Natal today is the Hypoxis angustifolia. It has small rhizomes with white flesh that is more palatable than the bitter, orange flesh of rhizomes from the better-known medicinal Hypoxis species incorrectly called African Potato.

“The rhizomes are rich in starch and would have been an ideal staple plant food,” Wits said in a statement on the team’s find.

According to the SA National Biodiversity Institute (SANBI), some of the Hypoxis plant’s species have long been used as African traditional remedies for the treatment of ailments such as urinary infections and nervous disorders. One species, the argentea, has small white rootstocks, which were boiled or roasted in times of famine as a source of food.

Wadley and Sievers made a collection of modern rhizomes and geophytes from the Lebombo area over four years. “We compared the botanical features of the modern geophytes and the ancient charred specimens, in order to identify them,” said Sievers.

The Border Cave site has been repeatedly excavated since 1934. Among earlier discoveries were the burial of a baby with a Conus seashell at 74,000 years ago, a variety of bone tools, an ancient counting device, ostrich eggshell beads, resin and poison that may once have been used on hunting weapons.