中国科学院南京地质古生物研究所机构知识库

The in situ spore ultrastructure of fossil Marattia asiatica (Kawasaki) Harris, a common Early Mesozoic marattialean fern in Asia, is investigated using scanning and transmission electron microscopes based on the material from the Lower Jurassic Hsiangchi Formation in Hubei, China. The exospore consists of a thin inner layer, a thick homogeneous outer layer, and an intermediate zone (middle layer). The intermediate zone comprises some very thin sheets linked to the inner layer and interbedded with sporopollenin similar to that composing the outer layer and includes small cavities connected to the wall surface through narrow canals crossing over the outer layer. No perispore elements were observed in the investigated spores. Comparisons of the exospore ultrastructures, especially those of the intermediate zone in extant and fossil ferns, indicate close affinities between fossil M. asiatica and the extant Marattiaceae. Such affinities are less evident for the Paleozoic fossil record of marattialeans, probably because of the less favorable preservation of the Paleozoic spores. Spore ultrastructure of fossil M. asiatica reveals one of the most primitive types reported so far among the fossil filicopsids. This represents the first ultrastructural study to date on the Mesozoic marattialean in situ spores, which provides significant information for the evolution between the Paleozoic ancestors and the extant marattialean members.