The Elements of Evolution (13-1) Ferns


Ferns are pteridophytes that emerged over 360 MYA. They were initially quite successful. Like sharks, ferns evolutionary advance was modest for 180 million years.

Unlike sharks, ferns could not compete with more modern designs. The towering of trees and rise of flowering plants foretold the demise of ferns.

Ferns were desperate for an innovation to save them from extinction. The answer lay in learning to live in the shadows of more advanced plants. Moving forward required looking back. The trick that let ferns live was genetically picked up from hornworts, an earlier-evolved non-vascular plant (bryophyte). Ferns co-opted the hornwort gene for making neochrome: a photoreceptive protein that lets ferns thrive on shady forest floors.

The green algae Mougeotia scalaris invented neochrome, which fuses red-sensing phytochrome and blue-sensing phototropin modules into a single molecule. Neochrome is efficiently receptive to longer wavelength light than chlorophyll, enlivening photosynthesis in relatively low light.

Hornworts – an early land plant – independently evolved neochrome a few times. Hundreds of millions of years later, ferns latched onto neochrome from hornworts via horizontal gene transfer.

This retro innovation gave ferns a new lease on life. From 180 MYA, the 1 lineage of ferns that managed to survive proliferated into 12,000 species.

The early Triassic, after the devastating Permian extinction 252 MYA, was the golden age of ferns. Ferns also flourished after the Cretaceous came to a crashing close 66 MYA. Their lithe appearance disguising a spunky spirit, ferns are early colonizers of barren landscapes.