Ancient ferns bum a ride off giant trees

DUKE (US)—During the Cretaceous period, ferns survived and flourished by getting a piggyback ride of sorts from giant trees that quickly rose to dominate plant communities.

Two key innovations may have led to the ferns’ success in the face of new competition from flowering plants, says Eric Schuettpelz, a researcher at Duke University, who is completing a post-doctoral fellowship in biology with associate professor Kathleen Pryer.

Some ferns developed the ability to make a living on light that was more toward the red end of spectrum—shade, in other words. And, around this time, some ferns also developed the ability to live on trees, sometimes without soil, as epiphytes, plants that grown on another plant or object that provides support, but not nutrients.

“The canopy is there and—boom—diversification,” Schuettpelz explains.

Though ancient, it appears that ferns really came into their own during a very hot, very wet period that peaked about 10 million years after the Cretaceous/Tertiary boundary 65 million years ago.

Schuettpelz and Pryer constructed a new time-calibrated family tree for ferns by integrating genomic data from 400 living fern species with information from the fossil record. Their study appears on the cover of the July 7 Proceedings of the National Academy of Sciences.

While the fossil record seemed to suggest that ferns experienced three distinct pulses of species diversification, the new research suggests there was a fourth, roughly corresponding with the development of epiphytism.

By storing water, developing thicker skin, or being more tolerant to drying out, the epiphytic ferns could now perch on a trunk, limb, or twig and live quite happily more than 100 feet off the forest floor, where moisture, temperature, and sunlight are very different.

So, as rain forests developed and tropical trees and vines clawed past each other to reach the sunlight above, ferns went along for the ride and thousands of new fern species evolved to take advantage of the new niches being created in the canopy.

“In some ways I guess, the epiphytes escaped the battle on the ground,” Schuettpelz says.

Today, epiphytes comprise about 30 percent of the more than 9,000 living fern species.

The study was supported by the National Science Foundation.

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