A 298-million-year-old gleicheniaceous fern from China

The late Paleozoic genera Chansitheca Regè, Oligocarpia Göppert and Szea Z. Yao et T. N. Taylor are small ferns that represent putative early members of the Gleicheniaceae based on their morphology and the anatomyof their fertile organs. However, the rachis and cauline anatomy are unknown, rendering their systematic affinities controversial. Here we document rachides with partly preserved anatomical structure associated with compression/impression specimens of Chansitheca wudaensis from the Wuda Tuff Flora. The in situ preservation of the flora, occasional organic connection and close association, and matching size, proportions and xylemstructure indicate that these rachides belonged to the same plant that produced fertile fronds of the Chansitheca wudaensis type and vegetative fronds of the Sphenopteris type co-occurring in this flora. The new details of the anatomy and morphology necessitate emendations to the diagnosis for this species. As the Wuda Tuff Flora has been dated to be 298.34 ± 0.09 million years ago (Asselian, Permian), this represents the oldest unequivocal evidence of Gleicheniaceae. Our results thus demonstrate that the Gleicheniaceae had already diverged from other ferns families, including the Osmundaceae, by this time.