Elucidating species richness in lichen fungi: The genusSticta(Ascomycota: Peltigeraceae) in Puerto Rico

Traditional taxonomic studies provide only a limited understanding of species richness within a group. Their usefulness for assessing species diversity could also be limited as many lack sufficient sampling and/or fail to integrate different data types for assessing species boundaries. To explore the challenges and limitations of estimating species richness in lichens, we employed an integrative taxonomic approach to elucidate diversification patterns of the genusSticta(Peltigeraceae) in Puerto Rico. Specimens were collected throughout the island, and a six-locus dataset was generated to infer phylogenetic relationships among Puerto RicanStictaand their continental counterparts. Phylogenetic analysis was combined with species delimitation methods and analysis of morpho-anatomical characters to assess diversity patterns and clarify species-level taxonomy. We found thatStictais represented by 16 species in Puerto Rico and that at least 11 (69%) of them are potentially endemic to the island. We describe eight of these in this work:S. borinquensissp. nov.,S. corymbosasp. nov.,S. densiphyllidiatasp. nov.,S. guilartensissp. nov.,S. harrisiisp. nov.,S. parvilobatasp. nov.,S. ripariasp. nov., andS. tainorumsp. nov. These species do not cluster in a monophyletic assemblage but are scattered over the broaderStictaphylogeny, indicating at least eight separate dispersal events. Putative endemic species were found to have close allies occurring in South America. Careful re-examination of material revealed phenotypical characters that separate most species, suggesting low levels of cryptic diversity. We highlight that integrating molecular methods and other sources of information in species discovery along with comprehensive sampling efforts can greatly enhance our knowledge about diversity patterns in poorly studied groups and regions. Furthermore, species and ecosystems in the Caribbean are being threatened by substantial human-driven changes (e.g., deforestation, climate change). Consequences of these impacts include reduction in already restricted habitats and potential extinction. We argue that studies analyzing species diversity within a phylogenetic framework could better inform conservation efforts aimed at addressing these challenges.