Two ferns that last shared an ancestor more than 60 million years ago have interbred — showing that this can still happen even after a long evolutionary gap.

Credit: Harry C. Roskam

As populations separate and evolve over time, they lose the ability to cross-breed. So Carl Rothfels, now at the University of California, Berkeley, and his team were surprised to find a fern (×Cystocarpium roskamianum; pictured) from the French Pyrenees that is a hybrid of Gymnocarpium and Cystopteris, two dissimilar genera. DNA analysis showed that its two parents diverged roughly 60 million years ago, the biggest known evolutionary gap in a plant or animal hybridization. This is comparable to a human interbreeding with a lemur.

The findings suggest that new species of fern evolve more slowly than many other plants, in part because they rely on wind and water for fertilization, making it harder for eggs and sperm of different species to remain separate.

Am. Nat. 185, 433–442 (2015)