An evidence-based 3D reconstruction of Asteroxylon mackiei, the most complex plant preserved from the Rhynie chert

The Early Devonian Rhynie chert preserves the earliest terrestrial ecosystem and informs our understanding of early life on land. However, our knowledge of the 3D structure, and development of these plants is still rudimentary. Here we used digital 3D reconstruction techniques to produce the first well-evidenced reconstruction of the structure and development of the rooting system of the lycopsid Asteroxylon mackiei, the most complex plant in the Rhynie chert. The reconstruction reveals the organisation of the three distinct axis types - leafy shoot axes, rootbearing axes, and rooting axes - in the body plan. Combining this reconstruction with developmental data from fossilised meristems, we demonstrate that the A. mackiei rooting axis - a transitional lycophyte organ between the rootless ancestral state and true roots - developed from root-bearing axes by anisotomous dichotomy. Our discovery demonstrates how this unique organ developed and highlights the value of evidence-based reconstructions for understanding the development and evolution of the first complex vascular plants on Earth.

Automated summary

This study used digital 3D reconstruction techniques to investigate the rooting system structure and development of the lycopsid Asteroxylon mackiei in the Early Devonian Rhynie chert. By combining this reconstruction with developmental data from fossilised meristems, the research demonstrates how the rooting axis of A. mackiei developed from root-bearing axes through anisotomous dichotomy, shedding light on the evolution of complex vascular plants on Earth.