Cordaitalean Seed Plants from the Early Permian of North China. I. Delimitation and Reconstruction of the Shanxioxylon sinense Plant

Abstract

A new whole plant species of cordaitalean coniferophyte is reconstructed from a single Early Permian coal‐ball assemblage in northern China and is named Shanxioxylon sinense after its distinctive stem. This assemblage contains three cordaitalean whole plants reconstructed from evidence, including organs found in organic connection and other examples where two or more organs share distinctive anatomical features. With the exception of the fertile shoot systems, organs of the S. sinense plant may be ascribed to existing cordaitalean morphogenera, although in each case they represent distinct morphospecies. Stems have a septate central pith and have previously been assigned to S. sinense. Primary vascular architecture is sympodial, and primary xylem maturation of the cauline bundles is endarch. Adventitious roots are infrequently observed on smaller stems. Leaf traces are mesarch, diverging from the pith margin as a single bundle and approaching 8/21 phyllotaxis. Leaves are small and needle‐like. Roots are protostelic and ditetrarch, while rootlets are protostelic and diarch, belonging to the morphospecies Amyelon taiyuanense. Both pollen and ovulate cones are assigned to Cathayanthus gen. nov., characterized by helically inserted bract/shoot complexes. Male shoot systems of Cathayanthus ramentrarus comb. nov. have pollen cones with 14–18 scales, of which three to five apical scales may be fertile. Fertile scales possess a ring of approximately five pollen sacs apically, which contain saccate prepollen of the Florinites type. Ovulate cones of Cathayanthus sinensis comb. nov. contain more than 100 scales with the distal half fertile, bearing a single terminal ovule. Ovules are bilaterally symmetrical and have a prominent wing, conforming to the morphospecies Cardiocarpus samaratus. Based on characters of the stem, roots, leaves, male and female shoot systems, and ovules, the S. sinense plant is distinct from other cordaitalean plants, although its features are consistent with models of cordaitalean morphology, anatomy, and architecture, indicating that it belongs to this group. The S. sinense plant shows that coniferophyte fertile shoot systems with vertically arranged rows of bract/shoot complexes can no longer be considered diagnostic of, or synapomorphic to, cordaitalean coniferophytes.