Unique growth strategy in the Earth's first trees revealed in silicified fossil trunks from China

The evolution of trees and forests in the Mid-Late Devonian Period, 393-359 million years ago, profoundly transformed the terrestrial environment and atmosphere. The oldest fossil trees belong to the Cladoxylopsida. Their water-conducting system is a ring of hundreds of individual strands of xylem (water-conducting cells) that are interconnected in many places. Using anatomically preserved trunks, we show how these trees could grow to a large size by the production of large amounts of soft tissues and new wood around the individual xylem strands and by a controlled structural collapse at the expanding base. We have discovered a complex tree growth strategy unique in Earth history, but with some similarity to that of living palms.