A new permineralized gymnospermous fossil stem, Parnaiboxylon wangi sp. nov., is described from the Moscovian Benxi Formation of Yangquan City, Shanxi Province, North China. It is composed of pith, primary and secondary xylems. The pith is solid, heterogeneous, with numerous secretory canals, ducts, and parenchymatous cells at the periphery. The primary xylem is endarch to mesarch. The secondary xylem is pycnoxylic, characterized by the presence of uni- to quariseriate araucarian radial tracheidal pitting, cupressoid to araucarioid cross-field pitting, and axial parenchyma. The fossil stem represents the fourth species of gymnosperms with anatomical features preserved from the Pennsylvanian of the Cathaysia. Anatomical characters, including solenoid pith and growth interruptions, and sedimentological evidence suggest a coastal environment with intermittent droughts or occasional incursions of seawater when the tree was alive. The presence of fungal hyphae, coprolites, and decayed tunnels in the secondary xylem of P. wangi sp. nov. indicate well-developed fungi–plant and animal–plant interactions when the Cathaysian flora at its early evolutionary stage.
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