Though tomatillos look a bit like tomatoes, they taste nothing like them. Also known as "ground cherries," these fruits are part of the diverse nightshade family, which includes everything from peppers and tobacco to tomatoes. Even so, scientists are largely still in the dark about their evolutionary origins.
The plants are fairly fragile, making it rare for them to fossilize. But while excavating a site in Argentina, a group of scientists from Pennsylvania State University struck botanic jackpot recently, uncovering a pair of fossil tomatillos—complete with their papery husks and the remains of their fleshy interiors. This find not only sheds new light on the tart but sweet fruit, but also suggest that they are much older than researchers once thought.
"These astonishing, extremely rare specimens of physalis fruits are the only two fossils known of the entire nightshade family that preserve enough information to be assigned to a genus within the family," Peter Wilf, a professor of geosciences at Penn State who led the study, says in a statement.
For years, researchers have tried to fill in the gaps using genetic analysis to try to estimate how early the nightshade family branched off. But these 52 million-year-old fossils are much, much older than scientists once thought based on genetic analysis, as Charles Davis, director of the Harvard University Herbaria tells Smithsonian.com.
“The ages for the nightshades was on the order of about 30 million years, and the tomatillo group is only about nine million years based on recent age estimates,” Davis says. “Here you have a fossil now within this tomatillo group that’s five times as old as what we thought.”
While molecular analysis can be a powerful tool for filling in evolutionary gaps in the data, Davis says that this find should be a wake-up call for researchers to remember that fossils are the best evidence for an organism’s age. Even so, this latest discovery doesn’t necessarily mean other nightshades are all older than once thought, Davis cautions.
“I’m not entirely convinced that their argument that the family is going to be much older holds,” Davis says. “There was no analysis and assessment of that." One possibility is that tomatillos could have diverged much more rapidly than expected.
For more definitive answers, researchers will need to find more fossils and do more in depth study of the plant's genetics. While these types of fossils are certainly rare, this recent discovery suggests more could still be hiding in the fossil record.
Even with more fossilized finds, however, it's unlikely that we'll ever know whether these ancient tomatillos would have made a good salsa.