New cyathealean tree fern, Yavanna chimaerica gen. et sp. nov., from the Early Cretaceous of Livingston Island, Antarctica

• Yavanna chimaerica gen. et sp. nov. is described from the Cerro Negro Formation.
• This taxon in referred to the Orden Cyatheales without clear familial placement.
• Yavanna shows a combination of features seen in different tree ferns.
• The already high number of Cyatheales described for the unit is increased.

A new genus and species of cyathealean fern, Yavanna chimaerica gen. et sp. nov., is erected for several permineralized stems recovered from the Early Cretaceous (Aptian) Cerro Negro Formation, which crops out at the South Shetland Islands, Antarctica. The new species is characterized by solenostelic erect stems with medullary bundles traversing the pith, and surrounded by persistent petiole bases and adventitious roots. Proximal petiole bases present a one-parted modified omega-shaped trace, which becomes three-parted distally. The anatomy of the new fern show similarities with both Thyrsopteris elegans Kunze and with the Cyatheaceae s.s., suggesting that it is a representative of an extinct lineage among the Cyatheales.