Our Science Editor Dr David Whitehouse explains the significance of Archaeopteris

The extinct plant called Archaeopteris made up most of the forests across the Earth about 370 million years ago.

The tree, like its modern counterparts, would have had a critical influence on the planet and its developing ecosystems.

It helped to filter out the high levels of carbon dioxide in the atmosphere of that time, altering the conditions on Earth and the evolution of all lifeforms.

Woody structures

Although the existence of Archaeopteris had been known about for many years, the poor quality of fossil specimens made it difficult to appraise its real significance.

Scientists were not sure if it looked more like a giant "weed" or a tree in the modern sense, with woody structures and lateral branches.

This has changed with the discovery of the largest group of anatomically well-preserved Archaeopteris remains ever found.

About 150 fossil specimens were found at three locations in ancient marine beds in south-eastern Morocco. The largest had trunks nearly 40 centimetres in diameter.

Trunk branching

Brigitte Meyer-Berthaud, Stephen Scheckler, and Jobst Wendt say they can see features in these fossils that confirm their belief that Archaeopteris is the earliest-known modern tree.

"It was the first time we had seen trunk branching on Archaeopteris, and we found hundreds of examples," Dr Stephen Scheckler says. "And we found big roots, which had previously been mostly conjecture."

From cell details of slices of trunks, Dr Meyer-Berthaud has shown that these ancient trees also had lateral buds on their trunks and branches.

"This was unique to Archaeopteris," says Scheckler. "It was the only plant at that time that could bud and continue growing after the main axis tip died; although seed plants now have that ability."

Long-lived trees

"The attachment of branches was the same as modern trees, with swelling at the branch base to form a strengthening collar and with internal layers of wood dovetailed to resist breaking," says Dr Scheckler.

"We had always thought this was modern but it turns out that the first woody trees on Earth had this exact same design."

Another unique feature of Archaeopteris was its long-life - some of the specimens were possibly 40 to 50 years old.

There are differences between Archaeopteris and modern trees, Dr Scheckler says. Archaeopteris reproduced by releasing spores rather than by producing seeds. That is one of the reasons why paleobotanists suspect that today's trees come from a sister line of plants, the "progymnosperms." Archaeopteris is more like an ancient aunt than a direct ancestor of modern trees.

The importance of Archaeopteris cannot be overstated, the scientists believe. Its influence on the planet would have opened up many new evolutionary avenues for new organisms to exploit.