The Formation of Geological Period and Modern Geographical Distribution Pattern of Lycophyte Selaginellaceae
Selaginellaceae is a monotypic lycophyte family.The genus Selaginella contains about 700 ex-tant species distributed all over the world.Selaginellaceae originated in the Devonian period,and the fossil record covers various geological periods from the Carboniferous period to the present.Several infrageneric systems of modern Selaginella have been proposed,however,research on the classification and geological history of Selaginellaceae fossils is still lacking.In the present review,time and geographical distribution of the fossil records were summarized,and the evolution and formation of the geographical distribution pattern were discussed in combination with molecular systematic studies,providing a reference for the tax-onomic and evolution studies of Selaginella.Based on the latest taxonomy and the fossil records,we sum-marized and determined the systematic taxonomy of fossils,and discussed the differentiation and geo-graphical distribution of subgenus Selaginella,subgenus Hexaphyllum and the rhizophoric clade.We concluded that Selaginellaceae originated in the Paleozoic Euramerican floral realm not later than the Per-mian,and spread to the Cathaysian and Gondwana floral realms along with the splitting of Pangea.The fossil subgenus Hexaphyllum was the basal group of the rhizophoric clade,which became extinct at the end of the Carboniferous.Fossil evidence showed that since the end of the Paleozoic,the rhizophoric clade might have become the dominant group of Selaginellaceae,and formed a global distribution pattern in the Mesozoic.
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