Abstract— We report Eryngium absconditum, a new species from Cordillera de Amambay, an area that belongs to the biodiversity hotspot of the Cerrado in Paraguay. The species was collected more than a century ago, but the collections remained unnoticed and misidentified until now. We describe, illustrate, and provide information on the geographical distribution and habitat of the new species. We also analyze and illustrate the morphological characteristics that differentiate it from Eryngium rojasii and E. paraguariense, the most similar species to the new. This study highlights the importance of Amambay as an area rich in endemic plant species and the need for continued taxonomic studies and the establishment of regional conservation policies for this region with its biodiversity under threat.

The species of Eryngium with a monocot-like habit are among the most taxonomically complex. They show low phenotypic and molecular differentiation due to their recent, rapid, and reticulate speciation during the Quaternary period. In this study, we evaluate the boundaries of the monocot-like Eryngium regnellii and a closely related entity from the grasslands in the Cerrado of Paraguay. We integrated evidence from multiple data sources to test species delimitation: we estimated the phylogenetic position of both entities within Eryngium based on ITS nrDNA and cpDNA sequences; we carried out univariate and multivariate morphometric analyses to test statistically significant differences and to recognize morphological diagnostic characters; we also analyzed geographic distribution, habitat, and bioclimatic variables to evaluate divergence in environmental niche, and finally, we used Bayesian coalescent-based delimitation approaches to test genetic structure. Divergence in morphology, environmental niche, and genetic structure between E. regnellii and the lineage from Paraguay support the hypothesis of evolutionary independence among these two lineages. Therefore, based on an integrative approach, we recognize and describe a new species from Paraguay: Eryngium cerradense.