Domestication is not always pretty. (“Modern cultivated tomatoes,” one author wrote in the food studies journal Gastronomica, “are a frail, inbred lot.”) Giant tomatoes bear little resemblance to their wild relatives and progenitors. The tomatillos, chief ingredient of salsa verde, lack a beefsteak crumple and are instead covered in a smooth papery sheath. That sheath, as it turns out, is much older than anyone expected: Researchers recently found a pair of husked fruit fossilized in Argentina, prompting experts to reevaluate the age of the tomato and tomatillo.
Called lantern fruits or groundcherries, the fossils belonged to the family Solanaceae, or the nightshades, wrote plant scientists from Cornell University, Pennsylvania State University and the Museum of Paleontology Egidio Feruglio, in Argentina, in the journal Science on Thursday. They named the plant Physalis infinemundi, meaning at the world’s end. The name was doubly significant, the authors noted: Infinemundi indicated contemporary Patagonia, at the tip of South America, where the fossils were uncovered. The plant also lived during the final stages of Gondwana, the supercontinent cluster that 52 million years ago connected parts of South America, Antarctica and Australia.
“Physalis sits near the tips of the nightshade family’s evolutionary tree, meaning that the nightshades as a whole, contrary to what was thought, are far older than 52 million years,” said Peter Wilf, a Pennsylvania State University geoscientist and study author, in a news release. Previously, experts believed that tomatillos only existed as recently as 9 million to 11 million years ago.
The nightshade family contains many children, some of which are quite popular. Several you would find in the supermarket produce aisle. Not just tomatillos and tomatoes, but potatoes and eggplants, too, belong to Solanaceae. The nightshades include a few other species located behind the cash register (tobacco) and flowers at home in a window box (petunias), as well as the relatives you will not find in most backyard gardens (the psychoactive belladonna plant, which sprouts berries so toxic that eating just two can kill a child).
At about an inch in diameter, the ancient lantern fruit better resemble a garnish, not something that could be placed in fat slices upon a burger. Given the delicate nature of the fruits, such fossils are rarely found. In addition to the lantern-shaped husk, the fruits had features typical of a Solanaceae plant, noted the researchers, such as veins that travel to the tips of the plant lobes.
“We exhaustively analyzed every detail of these fossils in comparison with all potential living relatives,” Wilf said, “and there is no question that they represent the world’s first physalis fossils and the first fossil fruits of the nightshade family.”
One fossil had the remnants of a berry that had turned to coal over the intervening millions of years. Wilf told The Washington Post by phone early Friday that “very, very few” other plants grew anything like the berry-and-husk combination of the ancient tomatillos. “It’s such a specialized structure,” he said. Using radiometric dating of igneous rock found around the fossils, the scientists pegged the plants at roughly 52 million years old.
The researchers found the fossils near Laguna del Hunco, a crater lake that would have been rain forest during the Eocene, an epoch that lasted from about 56 million to 34 million years ago. Much of the Patagonian environment is harsh or arid, including Laguna del Hunco. But at the time of the lantern fruit it would have been wetter and warmer — in fact, the scientists hypothesize similar plants once grew where today is Antarctic ice.
A humid, lakeside environment could also explain why plants like tomatillos evolved husks. It was possible that the papery shells acted as flotation devices, protecting the berries and seeds as they bobbed along a watery surface. To that end, the researchers tested modern tomatillos in a kitchen sink and stream. “Sure enough,” Wilf told The Post, the husks formed “a little air pocket that keeps the berry dry.”
The husk lived on for the tomatillo, but somewhere along the line, the wild ancestors of tomatoes, Solanum pimpinellifolium — colloquially, “pimps” — lost it. These tomato cousins, about the size of a pea, can found today in Peru and Ecuador. Agricultural scientists hope to exploit the pimps’ genes to restore flavor to supermarket tomatoes, bred for size and shelf life at the cost of taste.