Abstract: Triplophyllum is a fern genus of about 30 species, distributed across the moist tropical forests of Madagascar, Africa, and the Neotropics. The genus presents significant taxonomic challenges due to a combination of high morphological variability and subtle morphological differences among species. In this study, we use a molecular phylogenetic analysis to identify evolutionary lineages in the Neotropics and assess morphological characters useful for species delimitation. Our sampling encompasses most regions where the genus occurs and includes three‐quarters of the currently recognized species. Our results show that neotropical Triplophyllum species form a single clade, whereas paleotropical species form two clades, and that the circumscriptions of some neotropical species need to be revised. Optimization of morphological characters on the molecular tree reveals extensive homoplasy in indument traits, highlighting the limitations of morphology alone for phylogenetic inferences in the genus. Three new species are supported by both molecular and morphological analyses, and are described herein: Triplophyllum atlanticum, Triplophyllum ctenitoides, and Triplophyllum dalyi. We also designate a neotype for Triplophyllum funestum, one of the most widespread neotropical species, whose original type has been missing since its description. Because of the intricate evolutionary history of Amazonian biodiversity, traditional morphological taxonomy often fails to appreciate the true species richness of the Amazon and lumps superficially similar lineages into a single species. Our findings reinforce the importance of an integrative approach using molecular and morphological evidence for resolving species delimitation in these cryptic lineages.

Key words: Amazonia, biodiversity, cryptic species, ferns, phylogeny, taxonomy