Despite becoming ubiquitous in almost every corner of the world, surprisingly little is known about the deep evolutionary history of the group of plants that gave rise to potatoes, tomatoes, and tobacco. Now, researchers have found just how far back these organisms go, with the discovery of a fossil relative that dates back to 52 million years ago, tens of millions of years older than previously thought.
The fossil belongs to a fragile berry of a plant known as a tomatillo, or ground cherry. They form fruit that is often surrounded by a thin, papery lantern, making it difficult for them to be fossilized. Members of the Physalis genus, they form a small branch of the nightshade family, which in turn includes many commercially important crops, from potatoes and petunias to chillies and aubergines.
“These fossils are one of a kind, since the delicate papery covers of lantern fruits are rarely preserved as fossils,” explains Mónica Carvalho, who co-authored the paper published in Science, in a statement. “Our fossils show that the evolutionary history of this plant family is much older than previously considered, particularly in South America, and they unveil important implications for understanding the diversification of the family.”
One of the two fossils of the fruits clearly show their papery lantern. Ignacio Escapa/Museo Paleontológico Egidio Feruglio
The only fossil fruits ever found from this family of almost 2,000 species of plants, the two specimens were discovered in a fossilized rainforest that once grew across Patagonia in South America. With a lack of available fossils for this group of plants, researchers have had to rely on molecular dates for when the nightshade plants first evolved, and had settled on the figure of around 35 to 51 million years old, while the tomatillo was thought to be a relative newcomer at only 10 million years old.
The modern ground cherry still has the distinctive fruit. punsayaporn/Shutterstock
This new discovery, however, completely changes this. The fossils, dating to 52 million years ago, show that the ground cherries are actually a relatively ancient branch of the nightshade family. “We exhaustively analyzed every detail of these fossils in comparison with all potential living relatives and there is no question that they represent the world's first physalis fossils and the first fossil fruits of the nightshade family,” says Professor Peter Wilf, from Pennsylvania State University.
The fossils underpin the need for researchers to be careful when deducing an organism's evolutionary age solely from molecular clocks.