Mesofossils with noeggerathialean affinity based on epidermal characteristics from the Mississippian (lower Carboniferous) of Gansu Province, northwestern China

Abstract

Three types of charcoalified mesofossils with anatomical structures are described from the Serpkhovian (Carboniferous) Jingyuan Formation in northwestern China. They are characterized by fragmental pinnules with apical teeth, dentate lateral margins, and simple stomatal apparati. Epidermal cells on both adaxial and abaxial surfaces are elongated trapezoidal with straight to slightly curved anticlinal walls. The first type has fan-shaped venation with veins extending into each apical tooth individually. Pinnules are amphistomatic. Stomatal apparati are rare on the adaxial surface, distributing sporadically on the apical part. On the abaxial surface, stomatal apparati are densely distributed in intercostal areas. Stomatal pores are oriented parallel to the veins. The second type is featured by the hypostomatic epidermis. Both adaxial and abaxial epidermis are not differentiated. The third type contains epidermis with clearly differentiated costal and intercostal areas. Adaxial and abaxial surfaces are similar in cell morphology and distribution. Pinnules are amphistomatic. Stomatal apparati are constrained within intercostal areas and are denser on the abaxial surface. Dome-shaped papillae are present on periclinal walls of cells in costal areas. These mesofossils are proposed to be of noeggerathialean affinity based both on the gross morphology and epidermal features. It is hypothesized that they represent three different taxa due to their distinct epidermal characteristics. In combination with macrofossil records from the same fossil interval, it confirms that noeggerathialeans were important components of Mississippian floras in China. The mesofossils reveal a probably higher diversity of this plant group than previously documented based only on macrofossils.