A whole calamitacean plant Palaeostachya guanglongii from the Asselian (Permian) Taiyuan Formation in the Wuda Coalfield, Inner Mongolia, China

Abstract

A new whole-plant species of a calamitacean, Palaeostachya guanglongii sp. nov., is described in a volcanic ash bed from the Cisuralian (lower Permian) Wuda Coalfield, Inner Mongolia, North China. It was an approximately 2–3 m high shrub-like plant growing in a peat-forming swamp. It is characterized by three-orders of axes. The stem (first-order axis) bifurcates, resulting in two equal-sized major branches (second-order axis); both axial orders conform to the morphotaxon Calamites cf. schützeiformis type with Arthropitys type anatomy. Each major branch bears numerous ultimate branches that are composed of vegetative and fertile branches. Vegetative branches bear the leaf Asterophyllites longifolius, while fertile branches bear A. longifolius leaves at proximal nodes and P. guanglongii sp. nov. strobili at distal nodes. Whorls of bracts and sporangiophores alternate in the strobili, with sporangiophores inserting slightly above the bract whorls. Four sporangiophores make up one whorl, with each sporangiophore bearing four sporangia, yielding in situ spores of the Calamospora type. The bifurcating stem is unique in Sphenopsida, potentially indicating the development of determinate branching in this group. Our findings also extend the knowledge of the morphological plasticity of a combination of anatomical features of the wood and interfascicular.