The fossil Gleicheniaceous ferns of China: Biodiversity, systematics, spore ultrastructure and evolution

The Gleicheniaceae is an ancient leptosporangiate fern family with fossil records dating back to the Palaeozoic. Fossil gleicheniaceous plants in China have received much attention and it has been suggested they play an important role for understanding the origin and evolution of the Gleicheniaceae. In this paper, the fossil diversity of gleicheniaceous plants is analyzed based upon systematic review of 27 species ascribed to six genera of fossils recorded from the Permo-Carboniferous to Cretaceous/Tertiary of China. The reproductive structures, including sori, sporangia, annuli and in situ spores (including their ultrastructure) are especially emphasized and discussed in a systematic and evolutionary context. The palaeogeographical distribution and stratigraphical ranges of these fossils are investigated based on detailed fossil records at the species level. Our study indicates that fossil gleicheniaceous plants in China have undergone evolutionary processes that include origin, decline, recovery and radiation, during different episodes from the Carboniferous to Cretaceous/Tertiary.