Ancient alga developed large size and complex structure independently of other plants.
A mysterious deep-ocean seaweed diverged from the rest of the green-plant family around 540 million years ago, developing a large body with a complex structure independently from all other sea or land plants. All of the seaweed’s close relatives are unicellular plankton.
The finding, published today in Scientific Reports1, upends conventional wisdom about the early evolution of the plant kingdom. “People have always assumed that within the green-plant lineage, all the early branches were unicellular,” says Frederik Leliaert, an evolutionary biologist at Ghent University in Belgium. “It is quite surprising that among those, a macroscopic seaweed pops up.”
There are only a few described species in this odd order of sea life, known as the Palmophyllales. All live at great depth, usually more than 80 metres below the surface. Five years ago, Leliaert was one of the team that first investigated the order’s genetics. But even though it looked superficially like many green algae, the seaweed turned out to be only very distantly related to any other macroscopic green algae or land plant2. At this point, the scientists could do little more than show that the species was very different.