Lichens may have evolved after plants colonised the land: Study

Lichens, composite organisms in which algae and fungi live together as one life form, may have come into existence much later in the Earth's history than previously thought, according to a study which suggests they evolved millions of years after plants colonised land.

The study, published in the journal Geobiology, noted that until now scientists thought lichens were some of the first organisms to start moving to land from aquatic habitats -- changing the planet's atmosphere and helping form the terrain for modern plants.

The researchers, including those from The Field Museum in the US, said the specific questions of when lichens evolved, and how many times fungi evolved the ability to form symbiotic relationships with algae remained contentious until now.

They said in this symbiotic relationship -- where two species live together and both benefit -- the specialised blue-green algae called cyanobacteria provided food, and the fungi wrapped around it creating a shelter.

They used available fossils to extrapolate when the family trees of lichen-forming fungi and algae came into existence, and compared these with the ages of fossil plants.

The researchers found that lichens likely evolved long after complex plants.

"Lichens aren't as old as we thought they were. They're a younger, newer sort of symbiosis and haven't been around forever, covering the earth long before there were plants and animals running around," said study co-author Matthew Nelsen from The Field Museum.

Nelsen said the pattern of modern lichens showing up on rocks dated before the arrival of plants doesn't indicate that lichens evolved before plants.

"It provides a snapshot into what was going on deep in time on Earth, and when some of these groups started appearing," said Nelsen.

The researchers said the discovery provides a clearer picture of the world in which complex plants evolved since lichens are known to grow on soil, making the ground wetter, and influencing the kind of nutrients present in soil.