Made in the Shade

Adaptable flora: Hymenophyllum jamesonii, an epiphytic fern found in neotropical rain forests.

Courtesy Eric Schuettpelz Ph.D. '07

As flowering plants like giant trees quickly rose to dominate plant communities during the Cretaceous period, the ferns that had preceded them adapted and thrived.

While modern tropical rain forests were becoming established, ferns climbed aboard, and experienced a flowering of their own species diversity.

"The canopy is there and—boom—diversification," says Eric Schuettpelz Ph.D. '07, a postdoctoral research fellow in biology working with associate professor of biology Kathleen Pryer Ph.D. '95.

By integrating genomic data from 400 living fern species with information from the fossil record, Schuettpelz and Pryer constructed a new time-calibrated family tree for ferns. Their study appeared in the Proceedings of the National Academy of Sciences of the United States of America.

Though in existence long before the Cretaceous period, ferns came into their own during a hot, wet period near its end, approximately 65 million years ago.

Two key innovations may have led to the ferns' success in the face of the new competition from flowering plants. Some ferns developed the ability to survive in the shade and to live on trees, without soil, as epiphytes.

By storing water, developing thicker skin, or being more resistant 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.

Earlier research on the fossil record suggested that ferns experienced three distinct pulses of species diversification. This analysis shows that there was likely a fourth, roughly corresponding with the development of epiphytism.

So, as rain forests developed and tropical trees and vines clawed past each other to reach sunlight, they took the ferns up along with them. Thousands of new fern species evolved to take advantage of all the new niches being created in the canopy.

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