CONICET | Buscador de Institutos y Recursos Humanos

The Rio Genoa Formation hosts the most diverse Early Permian flora in western Gondwana. The fern diversity described from the unit surpasses that of most other Early Permian Gondwanan floras and includes fronds of Asterotheca, Dichotomopteris, Pecopteris, Sphenopteris, Oligocarpia, Cladophlebis, Corynepteris/Alloiopteris, and stem impressions (Caulopteris, Artisophyton). Among these, marattialean ferns are represented by five previously described species, originally assigned to Asterotheca. Paleozoic Marattiales are well documented in the Northern Hemisphere, where their taxonomy is well circumscribed. In contrast, Southern Hemisphere Marattiales have not been fully explored, which excludes key taxa from studies seeking taxonomic resolution in the group. Based on new collections from the Rio Genoa Formation, we describe a new marattialean fern represented by fertile and vegetative frond segments. The fronds are at least bi-pinnate and all frond segments display alternate divergence. Strongly decurrent ultimate pinnae bear 14-17 obovate pinnules with weakly lobed margins and broadly cuneate base. The decurrent pinnule midvein extends and bifurcates in the pinnule tip and the basal three lateral veins bifurcate once close to their base. Fertile pinnules hold 3-8 bulbous synangia which become stellate at maturity, with six radially arranged fusiform sporangia. This character combination places the Rio Genoa specimens among late Paleozoic marattialeans, and the pinnule shape and venation distinguish them from other Marattiales reported from this unit. This study marks a first step in renewed efforts to reconcile the taxonomy of Upper Paleozoic ferns from Rio Genoa with the most recent taxonomic treatments for the group.

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