A new fossil Acmopyle with accessory transfusion tissue and potential reproductive buds: Direct evidence for ever‐wet rainforests in Eocene Patagonia

• Published in: American journal of botany 2023-08, Vol.110 (8), p.1-n/a
• Main Authors: Andruchow‐Colombo, Ana, Rossetto‐Harris, Gabriella, Brodribb, Timothy J., Gandolfo, María A., Wilf, Peter
• Format: Article
• Language: English
• Subjects: accessory transfusion tissue (ATT); Acmopyle; conifers; Drought; Early Eocene Climatic Optimum; Eocene; Flora; Fossils; Herbivory; insect damage; Insects; Laguna del Hunco; Leaves; New species; Paleocene; Phylogenetics; Phylogeny; Plant cuticle; Podocarpaceae; Rainforests; reproductive buds; seed cone development; Shoots; Taxonomic revision; Tissues; total evidence phylogeny; Transfusion
• ISSN: 0002-9122; 1537-2197
• DOI: 10.1002/ajb2.16221

Premise Acmopyle (Podocarpaceae) comprises two extant species from Oceania that are physiologically restricted to ever‐wet rainforests, a confirmed fossil record based on leaf adpressions and cuticles in Australia since the Paleocene, and a few uncertain reports from New Zealand, Antarctica, and South America. We investigated fossil specimens with Acmopyle affinities from the early Eocene Laguna del Hunco site in Patagonia, Argentina. Methods We studied 42 adpression leafy‐shoot fossils and included them in a total evidence phylogenetic analysis. Results Acmopyle grayae sp. nov. is based on heterophyllous leafy shoots with three distinct leaf types. Among these, bilaterally flattened leaves uniquely preserve subparallel, linear features that we interpret as accessory transfusion tissue (ATT, an extra‐venous water‐conducting tissue). Some apical morphologies of A. grayae shoots are compatible with the early stages of ovuliferous cone development. Our phylogenetic analysis recovers the new species in a polytomy with the two extant Acmopyle species. We report several types of insect‐herbivory damage. We also transfer Acmopyle engelhardti from the middle Eocene Río Pichileufú flora to Dacrycarpus engelhardti comb. nov. Conclusions We confirm the biogeographically significant presence of the endangered West Pacific genus Acmopyle in Eocene Patagonia. Acmopyle is one of the most drought‐intolerant genera in Podocarpaceae, possibly due to the high collapse risk of the ATT, and thus the new fossil species provides physiological evidence for the presence of an ever‐wet rainforest environment at Laguna del Hunco during the Early Eocene Climatic Optimum.