A new study titled “Why Plants Were Terrestrial From The Beginning” and published in the journal Trends in Plant Science by Danish scientists suggests that land plants actually evolved from land – long before they were thought to have migrated from aquatic algae.
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The original understanding from earliest studies was that land plants evolved from green algae which floated inland and began growing on land, giving rise to ferns, flowers, and trees. But the Danish scientists disagree, citing genetic evidence that land plants grew out of green algae existent on land and not from water.
Jesper Harholt of Carlsberg Laboratory, and Øjvind Moestrup and Peter Ulvskov, both of University of Copenhagen relied morphological and genetic proofs to establish facts that traits of land plants can today be found in some species of green algae.
"We realized that algae have a cell wall that's similarly complex to terrestrial plant cell walls, which seemed peculiar because ancient algae were supposedly growing in water," said Harholt. "We then started looking for other traits that would support the idea that algae were actually on land before they turned into land plants."
Analyzing the evolution of plant cell wall – which is regarded crucial for survival on land, the researchers found that green algae together with land plants share certain genes responsible for tolerance to light and drought.
In his 1908 article titled “The Origin of a Land Flora,” botanist Frederick Orpen Bower had argued that land plants migrated from aquatic algae. But this latest study overturns that article with more evidence, and the Danish researchers are still looking for more genetic proofs in fossils to substantiate their position in this debate.
"With all of the genomic and morphological data we have, it is very hard to explain, evolutionarily-wise, how algae lived in water all the way up to land plants," said Ulvskov, also with Copenhagen's Department of Plant and Environmental Sciences. "We have to turn this thinking on the head--we have the evidence now."
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Evolutionary biologist Moestrup wonders how green algae could have been terrestrial from time immemorial when a handful of species are around today, stating that they could have been outcompeted out of existence and that researchers may come across their genetic traits one day in aquatic plant fossil studies.