The Phylogenetic Position of the Fossil: Polystichum espinarensis sp. nov. Reveals Its Relationship with an Exindusiate Andean Clade

Aliaga-Castillo A.; León B.; Sanín D.; Martínez C. · International Journal of Plant Sciences (2026) · DOI: 10.1086/738641

Resumen

Premise of research. Polystichum (Dryopteridaceae), the third-largest fern genus in the world, is globally distributed, and tropical America is one of its main centers of diversity. Molecular evidence suggests that Polystichum diverged during the Eocene. Tropical America, the Greater Antilles, Mexico, and the northern and central Andes are its centers of diversity. The discovery of a new fossil from the early Pliocene of the Central Andean Plateau (CAP) in Peru provides evidence for understanding the divergence of the Andean lineage. Methodology. The fossil specimen was compared to extant species of Dryopteridaceae and previously documented fossil records through a review of herbarium specimens and literature. To estimate the phylogenetic position of the fossil, we conducted a scaffold phylogenetic analysis using maximum parsimony. The morphological information used in the analysis was gathered in a matrix that contained 30 frond and sporangial characters for 29 taxa, including the fossil under study; 25 extant species of Polystichum; and three outgroups’ species. Once placed in the phylogeny, the fossil was formally described. Pivotal results. The scaffold phylogenetic analysis placed the fossil within clade III of exindusiate Andean Polystichum. We described and named the fossil Polystichum espinarensis sp. nov. We revisited the earlier fossil record of Polystichum bolivianum Berry and concluded that its proposed affinity lacks sufficient morphological evidence. Therefore, P. espinarensis is proposed as the only fossil record known for the genus. Conclusions. This study sheds light on the diversification and biogeographic history of Andean Polystichum, indicating that P. espinarensis was already present in the early Pliocene. Its diversification, particularly among exindusiate Andean Polystichum species, was likely driven by the Pliocene uplift of the CAP.

Instituciones: Universidad Nacional Mayor de San Marcos