Deep in the El Castillo cave in northern Spain, up a side passage off the main pathway, there is a small painted panel most visitors would walk straight past.

Created some 17,000 to 15,000 years ago, it shows five red signs, each shaped a little like a bell. A natural stone ledge runs beneath them like the lip of an altar. For over a century, archaeologists have simply catalogued these as “bell-shaped signs”, filed under the vast heading of ice age marks we don’t know the meaning of.

Building on my PhD research surveying plants used in shamanic ritual worldwide, I argue they may be flowers. Mind-altering flowers, to be specific – the bell of a psychoactive nightshade, most likely belladonna or a local henbane.

I published a paper in 2021 making a similar case for a tree drawn on the Chu Silk Manuscript, China’s oldest illustrated text. I read this tree as a plant credited in early Chinese herbals with letting its user see and speak with spirits.

If my interpretation is correct, then these unremarkable red signs would be the oldest known picture of a mind-altering plant anywhere in the world, by thousands of years. And it could be corroborated the way it was at Pinwheel Cave in California, where chewed bits of hallucinogenic plant matter found wedged into the rock gave the first unambiguous physical proof anywhere in the world that a plant depicted in rock art had been ingested at the site.

Look at a belladonna flower and then at the signs, and the resemblance is hard to........

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