Plants crawled onto land earlier than we give them credit, genetic evidence suggests
Plant biologists agree that it all began with green algae. At some point in our planet’s history, the common ancestor of trees, ferns, and flowers developed an alternating life cycle–presumably allowing their offspring to float inland and conquer Earth. But on December 16 in Trends in Plant Science, Danish scientists argue that some green algae had been hanging out on land hundreds of millions of years before this adaptation and that land plants actually evolved from terrestrial, not aquatic, algae.
Botanists have suspected this possibility since 1980, but supporters have lacked proof. Now, Carlsberg Laboratory’s Jesper Harholt and University of Copenhagen’s Øjvind Moestrup and Peter Ulvskov present genetic and morphological evidence that corroborates the theory. Notably, traits that land plants use to survive on land today are well conserved in some species of green algae.
“The strange thing for me is that if these green algae were terrestrial for a long time, how come that so few of these species are still around?” says Moestrup, an evolutionary biologist. “It could be because they were all outcompeted, but maybe one day we will find more green algae of this lineage.”More.
Hundreds of million of years is a long time. The Cambrian period was only about 550 million years ago. So was there a sudden “Big Bang” of green plants on land as well?
Stasis: Life goes on but evolution does not happen
See also: Not a Big Bang of turtles too? Evolved “very rapidly” rather than slowly over vast stretches of time.
Insects, in general, earlier than thought?
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Here’s the Summary
The current hypothesis is that land plants originated from a charophycean green alga and that a prominent feature for adaptation to land was their development of alternating life cycles. Our work on cell wall evolution and morphological and physiological observations in the charophycean green algae challenged us to reassess how land plants became terrestrial. Our hypothesis is simple in that the charophycean green algae ancestors were already living on land and had been doing so for some time before the emergence of land plants. The evolution of alternate life cycles merely made the ancestral land plants evolutionary successful and had nothing to do with terrestrialization per se. (public access) – Jesper Harholt, Øjvind Moestrup, Peter Ulvskov. Why Plants Were Terrestrial from the Beginning. Trends in Plant Science, 2015; DOI: 10.1016/j.tplants.2015.11.010