Ancient algae offers clues about where plants came from

These prehistoric algae specimens exhibit many traits seen today in green seaweeds.

Rick Docksai | Mar 28, 2020

How the first plants emerged on dry land on the prehistoric Earth has long been a mystery: They, like all life, existed only underwater billions of years ago, according to researchers. But some recent studies of molecular biology and an ancient algae fossil suggest a few clues.

According to researchers, the first plant life to transition out of water and onto land may have evolved from some form of seaweed and most likely had soft, mossy textures and shallow roots. Such plants don't preserve well in fossils.

However, one recent find is an exception: an algae specimen in China that appears to be a billion years old, making it the oldest known specimen of green algae on Earth. It is 200 million years older than the previously oldest known algae fossil, which researchers had dated back to 800 million years ago.

"It's very daunting. A billion yearsthat's at least five times older than the oldest dinosaurs," said Shuhai Xiao, a Virginia Polytechnic Institute and State University geobiology professor and senior author of a paper announcing the discovery. "It's before any animals. The world is very, very different from what we know today."

These prehistoric algae specimens exhibit many traits seen today in green seaweeds: They were photosynthetic, multicellular, and had leaves and branches.

But the transition to dry land may have come even earlier, suggests another recent paper in Cell. University of Alberta biologist Gane Ka-Shu Wong and coauthors present evidence that the closest living relatives to land plants are a mossy freshwater species, Zygnematophyceae, which is single-celled. The adaptations plants need for dry land may have come about before the ancient algae specimens, the authors conclude.