Is the origin of terrestrial plants in terrestrial and not marine algae as believed until now?

"We noticed that algae have a cell wall whose complexity is strikingly similar to the complexity of the cell wall of terrestrial plants, a fact that seemed strange to us in light of the common hypothesis that ancient algae supposedly grew in water," says the lead researcher. In the next step, we began to examine other characteristics that could support the hypothesis that algae actually developed on land before becoming land plants."

[Translation by Dr. Nachmani Moshe]
Biologists who specialize in plants all agree that it all started with green algae. At some point during the history of our plants, the common ancestor of trees and flowers began to develop an alternate life cycle - allowing their descendants to conquer the earth. However, scientists now claim that several types of green algae had already settled on land hundreds of millions of years before this adaptation and that in fact the land plants evolved from terrestrial algae, not marine.

Scientists from Denmark claim, in their article published in the scientific journal Trends in Plant Science, that several types of green algae had already settled on land hundreds of millions of years before their adaptation and that in fact the land plants evolved from terrestrial algae, not marine. Botanists have suspected this possibility since 1980, but the supporters of this hypothesis have not been able to provide the necessary evidence for this. Now, researchers at the University of Copenhagen in Denmark present genetic and morphological evidence that confirms this theory. The research began when the scientists examined the development of the plant cell wall, which has long been considered an important stage of adaptation to a terrestrial lifestyle, since it is the one that provides physical support for plants growing under the influence of gravity.

"We noticed that algae have a cell wall whose complexity is strikingly similar to the complexity of the cell wall of terrestrial plants, a fact that seemed strange to us in light of the common hypothesis that ancient algae supposedly grew in water," says the lead researcher. In the next step, we began to examine other characteristics that could support the hypothesis that algae actually developed on land before becoming land plants." The researchers examined structures, or rather, the absence of structures, which are difficult to explain if the algae lived only in water. For example, some green algae have lost their flagella, those whip-like organelles that help single-celled organisms move through water. All types of algae that are close to land plants have lost their pupil, the organ that helped them swim towards a point of light.

The data on the characteristics of the cell wall together with the details of the genome floor of a terrestrial green alga (Klebsormidium) that were recently published, revealed that the green alga has several genes in common with land plants, genes related to light and drought tolerance. "When we had the genetic information, we were able to determine that the traits grew linearly, and not through convergent evolution," notes the researcher. If the researchers' theory is able to withstand a thorough and thorough criticism, it will be able to receive confirmation of what has been mentioned with skepticism in the textbooks for over a hundred years. The idea that the plants jumped from the water to the land was put forward by the botanist Frederick Orpen Bower, although it is not clear if this was the argument he was referring to. In 1908 he published a book called "The Origin of Land Plants" where he raised the idea of ​​such a possibility.

"In light of all the genetic and morphological data we have, it is very difficult to explain, from an evolutionary point of view, exactly how the algae that lived in water did the entire route until they became terrestrial plants," says the researcher. The most complex challenge facing the researchers is to prove that there was indeed a period of pre-adaptation that led to the formation of a complex cell wall in land plants. The researchers believe that these terrestrial green algae were advanced enough to survive in sandy areas, where the rain itself provides them with a source of moisture and water. Given the fact that there are very few, if any, fossils from this period, researchers will have to rely on genetic data to support their argument.

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