Ferns are often considered the 8-tracks of the plant world--they had their heyday in another era, and now linger in obscurity. But the lacy-leaved plants may not be as passé as previously thought. New analyses suggest that a major evolutionary expansion for ferns came in the wake of the flowering plants and may actually have been precipitated by their showy debut.
The fossil record is chock-full of angiosperms, a testament to the extraordinary explosion of flowering plants that began around 140 million years ago. Today, angiosperms boast a diversity of 250,000 to 300,000 species, compared to 10,000 kinds of ferns. Ferns once dominated the landscape, as early as 300 million years ago, but they apparently became more scarce in the Cretaceous. Scientists attributed the ferns' demise to the coincident rise of their more sophisticated relatives. "People have this general idea that ferns are holdovers and are just hanging on," says team member Kathleen Pryer of Duke University.
However, that assumption may owe less to hard evidence than to researchers' tendency to focus more on flowering plants and difficulties in classifying fossil ferns. To skirt these potential biases, Pryer and several colleagues looked at fossil and molecular data to estimate when particular branches of the family trees diverged. Rather than cowering in the shadows of flowering plants, many ferns seem to have diversified, they report in the 1 April issue of Nature. Most major lineages of polypod ferns, which comprise more than 80% of today's fern species, arose and diversified a mere 100 million years ago, after the major riot of flowering plants.
The spread of flowering plants must have greatly altered the landscape, and the scientists suggest this provided a multitude of ecological nooks and crannies, ripe for colonization by ferns. "The idea that the polypods took advantage of the angiosperms-- that's hot!" says David Barrington of the University of Vermont in Burlington. It appears that the notion that ferns are just evolutionary relics may be a relic itself.