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Premise: Eocene floras of Patagonia document biotic response to the final separation of Gondwana. The conifer genus Araucaria, distributed worldwide during the Mesozoic, has a disjunct extant distribution between South America and Australasia. Fossils assigned to Australasian Araucaria Sect. Eutacta usually are represented by isolated organs, making diagnosis difficult. Araucaria pichileufensis E.W. Berry, from the middle Eocene Río Pichileufú (RP) site in Argentine Patagonia, was originally placed in Sect. Eutacta and later reported from the early Eocene Laguna del Hunco (LH) locality. However, the relationship of A. pichileufensis to Sect. Eutacta and the conspecificity of the Araucaria material among these Patagonian floras have not been tested using modern methods. Methods: We review the type material of A. pichileufensis alongside large (n = 192) new fossil collections of Araucaria from LH and RP, including multi‐organ preservation of leafy branches, ovuliferous complexes, and pollen cones. We use a total evidence phylogenetic analysis to analyze relationships of the fossils to Sect. Eutacta. Results: We describe Araucaria huncoensis sp. nov. from LH and improve the whole‐plant concept for Araucaria pichileufensis from RP. The two species respectively resolve in the crown and stem of Sect. Eutacta. Conclusions: Our results confirm the presence and indicate the survival of Sect. Eutacta in South America during early Antarctic separation. The exceptionally complete fossils significantly predate several molecular age estimates for crown Eutacta. The differentiation of two Araucaria species demonstrates conifer turnover during climate change and initial South American isolation from the early to middle Eocene. [ABSTRACT FROM AUTHOR]

The 51.9 Ma Laguna del Hunco (LH) and 47.5 Ma Río Pichileufd (RP) floras from Patagonia, Argentina are unusually rich, angiosperm-dominated assemblages with living relatives in the low-latitude West Pacific, neotropics, and temperate southern latitudes. The diverse gymnosperms in these floras are important for Gondwanan biogeographic history and paleoclimatic interpretations. "Libocedrus" prechilensis Berry 1938 (Cupressaceae), previously known only from the holotype (RP), a vegetative branch, is revised here based on new material from both localities, including a seed cone attached to a shoot with cuticle (LH). Characters of these fossils are diagnostic of monotypic Papuacedrus (highlands of New Guinea and Moluccas). Living P. papuana is most abundant in cloud forests receiving up to 4 m rainfall annually, whereas Austrocedrus (Libocedrus) chilensis, the basis of comparison when the fossil species was named, inhabits dry, cold steppe margins to mediterranean climates in southern South America. We establish Papuacedrus prechilensis comb. nov., which simultaneously invalidates a southern South American connection for the fossil floras and reveals a link to West Pacific montane rainforests. Combined evidence indicates a biome similar to extant subtropical, or tropical montane, rainforests that persisted for at least 4.4 Myr, linking elevated floral richness to abundant rainfall. [ABSTRACT FROM AUTHOR]