Microlepia burmasia sp. nov., a new fern species from mid-Cretaceous Kachin amber of norther Myanmar (Dennstaedtiaceae, Polypodiales)

The rise of angiosperms during the Cretaceous was thought to be related to the radiation of polypod ferns, a fern lineage that represent 80% of the modern fern diversity. However, although the proposed palo-diversity from DNA based studies, Mesozoic polypod fern fossils with preserved fertile pinnae are scarcely. Here, we investigated the fragment of polypod fern preserved in mid-Cretaceous Kachin amber from northern Myanmar and assigned a new fossilized fertile pinnule into the genus Microlepia (Dennstaedtiaceae), described as Microlepia burmasia Long, Wang and Shi, sp. nov. The new species is mainly characterized by the 2-pinnate-pinnatifid pinnule with surface and margin covering short tomentum and articulate hairs. Vein free, pouch-shaped indusia, submarginal and terminal on one vein of sori, sporangium with interrupted, vertical annulus and spores trilete. This discovery adds to polypod fern diversity in the Cretaceous and dates the origin of Microlepia to at least 60 million years earlier, which is evidence for an early origin of polypod ferns and coincides with the rise of angiosperms.