RT Journal Article SR Electronic T1 An evidence-based 3D reconstruction of Asteroxylon mackiei the most complex plant preserved from the Rhynie chert JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.04.11.439326 DO 10.1101/2021.04.11.439326 A1 Hetherington, Alexander J. A1 Bridson, Siobhán L. A1 Jones, Anna Lee A1 Hass, Hagen A1 Kerp, Hans A1 Dolan, Liam YR 2021 UL http://biorxiv.org/content/early/2021/04/11/2021.04.11.439326.abstract AB The 407-million-year-old 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 complete reconstruction of the lycopsid Asteroxylon mackiei, the most complex plant in the Rhynie chert. The reconstruction reveals the organisation of the three distinct axes types – leafy shoot axes, root-bearing 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 plants on Earth.Competing Interest StatementThe authors have declared no competing interest.