Pleurorhizoxylon yixingensegen. et sp. nov., a Euphyllophyte Axis with Anatomically Preserved Adventitious Roots from the Late Devonian of South China

Abstract

Premise of research. Rooting structures were major contributors to Devonian global change, but anatomically preserved plant roots are rare from this period. We report a new type of plant axis from the Upper Devonian strata of South China that contains a protostele, relatively extensive secondary xylem and adventitious root traces. Methodology. The original specimens were fragmentary coalified axes, most of which were embedded in Epon resin, sectioned transversely and longitudinally, and ground into thin sections. The sections were observed and imaged with the light microscope. A few were observed directly with a Scanning Electronic Microscope (SEM). Pivotal results. The axis of this new plant, named Pleurorhizoxylon gen. nov., consists of a three-ribbed protostele and thick secondary xylem; the primary xylem is of apparent mesarch maturation, with a single protoxylem lacuna near the end of each rib. The secondary xylem has variable rays composed of parenchyma cells and has scalariform to elliptical bordered pits on both radial and tangential walls of the tracheids. The adventitious root traces are located opposite each primary xylem rib going through the wood, they are accompanied by large rays and cause significant accommodation (knotting) in the wood. Extra-xylary portions are poorly preserved, and no cambium or secondary phloem has been found. Conclusion. The new plant has a unique combination of characters and demonstrates the anatomical basis for adventitious root growth present in a Devonian moniliform plant for the first time.

The limits of life revealed in a silicified micro-ecosystem: Sphenophyllum stems, leaves, and roots trapped inside an arthropod boring in a Permian calamitalean

“…While the Pennsylvanian/Permian forms seem to share groups of crowded elliptical to circular bordered pits (e.g., RENAULT 1873, WILLIAMSON & SCOTT 1895, BAXTER 1948, CICHAN 1985, the Mississippian forms show scalariform pits (GALTIER 1970, TERREAUX DE FELICE et al 2019). However, the oldest known sphenophyllalean forms with preserved anatomy from the Late Devonian of China, such as Hamatophyton LI et al 1995, Rotafolia WANG et al 2005, and Pleurorhizoxylon ZHANG 2018 show various transitions from radially elongated "scalariform" to multiscalariform or elliptical bordered pits (LI et al 1995, DE-MING WANG 2005, ZHANG et al 2018. In S. plurifoliatum, not only the secondary xylem but also the metaxylem shows elliptical bordered pits (BAXTER 1948).…”

Peer Review #1 of "Keraphyton gen. nov., a new Late Devonian fern-like plant from Australia (v0.1)"

“…Five sphenophyllalean genera of Late Devonian age from the Hubei and Zhejiang provinces of China (South China plate) and Belgium (Laurussia) are represented by specimens that are partly or entirely preserved in anatomy (Ma, Liao & Wang, 2009 (Brongniart, 1828;Stockmans, 1948;Wang et al, 2006a;Wang et al, 2006b;Zhang et al, 2018;Terreaux de Félice, Decombeix & Galtier, 2019). Sphenophyllalean axes share two characters with Keraphyton, a ribbed protostele and a primary xylem maturation that may be exarch.…”