The oldest land plants just got a lot older. Generally considered to date back 450 million years, land plants may actually have been around 300 million years or more before that, according to a report in the 10 August issue of Science. Moreover, land-based fungi and green algae could have evolved more than 1 billion years ago.
Biologists have long wondered about the identity of the first terrestrial botanical pioneers. Many suspect that these land-lovers were fungi living in association with microbial plants, although there's scant fossil evidence earlier than 450 million years ago.
To nail down the origins of the first land plants, S. Blair Hedges, an evolutionary biologist at Pennsylvania State University, University Park, and colleagues took a molecular approach. They compared the amino acid sequences of 119 proteins from a wide variety of fungi, a moss, a higher plant, a green alga, and two yeast species to build a family tree of these organisms. The results indicated that the first terrestrial fungi appeared 1.3 billion years ago, not 660 million to 370 million years ago, as previously reported. And with the origin of plants pushed back to 750 million years ago, Hedges proposes that early plants contributed to the sudden rise in oxygen and the widespread glaciation that occurred some 650 million years ago.
These new results are surprising and convincing, says Linda Graham, a plant evolutionary biologist at the University of Wisconsin, Madison. "This is probably the most complete study [dating land plants] that I know of," she adds.