The fossilized remains of a tree that lived 374 million years ago suggest that the earliest trees we know of might also have been the ones with the most complex internal structure in the history of our planet.
The study, published in the Proceedings of the National Academy of Sciences, focused on the fossils of cladoxylopsids. While trees today have a central vascular system called a xylem at their center, these ancient specimens had multiple xylems located in the outer 5 centimeters (2 inches) of the trunk.
The international team of researchers say this distribution suggests that those trees grew in a different way than their modern counterparts. Nowadays, trees grow rings around their central xylem, with each ring usually representing a year of its life. In the ancient cladoxylopsids, rings grew around every single xylem. The scientists point out that this looks like they are multiple trees inside a single one.
“There is no other tree that I know of in the history of the Earth that has ever done anything as complicated as this," co-author Dr Chris Berry from Cardiff University said in a statement. "The tree simultaneously ripped its skeleton apart and collapsed under its own weight while staying alive and growing upwards and outwards to become the dominant plant of its day.
“By studying these extremely rare fossils, we've gained an unprecedented insight into the anatomy of our earliest trees and the complex growth mechanisms that they employed.
"This raises a provoking question: why are the very oldest trees the most complicated?”
Dr Berry has worked on many different fossilized trees and forests, but has maintained a particular focus on cladoxylopsids for nearly 30 years. For a long time, the fossils were but fragments, until a well-preserved cladoxylopsids tree trunk was uncovered in north-west China.
“Previous examples of these trees have filled with sand when fossilized, offering only tantalizing clues about their anatomy," Dr Berry added. "The fossilized trunk obtained from Xinjiang was huge and perfectly preserved in glassy silica as a result of volcanic sediments, allowing us to observe every single cell of the plant."
While the researchers focus on trees and their growth, there is also another interesting angle. Berry hopes to understand how much carbon dioxide these trees were capable of storing and how this impacted the climate.