For most plants and animals, reuniting after such a long hiatus is thought to be impossible due to genetic and other incompatibilities between species that develop over time.

"Reproducing after such a long evolutionary breakup is akin to an elephant hybridizing with a manatee or a human with a lemur," said study co-author Kathleen Pryer, director of Duke University Herbarium.

The genetic analyses revealed that the fern was the result of a cross between an oak fern and a fragile fern - two distantly related groups that co-occur across much of the northern hemisphere but stopped exchanging genes and split into separate lineages some 60 million years ago.

"To most people they just look like two ferns, but to fern researchers these two groups look really different," Rothfels said. Other studies have documented instances of tree frog species that proved capable of producing offspring after going their separate ways for 34 million years, and sunfish who hybridized after nearly 40 million years, but until now those were the most extreme reunions ever recorded.

"For most plant and animal species, reproductive incompatibility takes only a few million years at the most," said co-author Carl Rothfels from the University of California, Berkeley.

The study appeared online in the journal American Naturalist.


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