Anatomical Study Of The Late Permian Selaginella From Fuyuan,Yunnan

Lycophytes initially appeared in the Devonian Period,and were proliferous in the Carboniferous and Permian,but gradually became deterioration since the Mesozoic,and comprise only three extant groups nowadays,i.e.Lycopodiales,Isoetales and Selaginellales.The diversity of lycophytes was low and only composed of herbaceous forms in the Devonian,but it reached the evolutionary acme in the context of both diversification and palaeogeographic distribution in the Carboniferous and Permian periods,particularly characterised by the occurrence of diverse arborescent forms that formed wide spread forests in the peat-forming habitats;after the end-Permian mass extinction,the arborescent lycophytes were completely disappeared,whereas the herbaceous forms survived and persisted to the present-day.Selaginella is the only genus of the lycophyte Oder Selaginellales,encompassing 600–800 species,and represents the most species-rich genus among the Plant Kingdom.However,due to the lack of fossil record,the biodiversity and the evolutionary history of Selaginella remains poorly understood.A large number of exceptionally well-preserved Selaginella leaf cuticles were obtained using bulk maceration methods from the Xuanwei Formation in Fuyuan County of Yunnan Province,Southwest China.After treatments of Schulze's reagent and Na OH,the morphology and anatomy of these cuticles were investigated in details using transmitted light microscopy and scanning electron microscopy in present thesis.The current fossil Selaginella leaves are microphylls,linear to ovate,with entire margins or short spines on leaf margins.The cuticles consist of subcircular or isodiametric polygonal epidermal cells showing straight anticlinal walls or undulate anticlinal walls;specialised idioblasts showing swollen periclinal walls are commonly present among the normal epidermal cells;stomatal complexes are formed by two kidney-shaped guard cells,amphistomatic or hypostomatic,irregularly distributed.Ac-cording to the morphological and anatomical characteristics,the current fossil cuticles were preliminarily assigned to nine fossil forms.In comparison with ten extant Selaginella species collected from Yunnan Province,the nine fossil forms do not necessarily represent nine individual biological species of Selaginella,but may represent different ontogenetic stages or different parts(i.e.medium,lateral or axillary leaf)of the same species with varying morphology,since none of the current fossil leaf organically attached to an axis.This is the first report of the epidermal anatomies of Selaginella leaves from the late Paleozoic Cathaysian flora.The present thesis is not only significant in the understanding of the biodiversity and evolutionary history of fossil Selaginella,but also provides new knowledge for the floristic composition of the Cathaysian flora.