Global species richness prediction for Pyrenulaceae (Ascomycota: Pyrenulales), the last of the “big three” most speciose tropical microlichen families

Together with Graphidaceae and Trypetheliaceae, Pyrenulaceae forms part of the "big three", the three most speciose, chiefly tropical microlichen families. Microlichens are the most diverse component of tropical lichen communities, with numerous species still to be discovered. Following previous analyses of Graphidaceae and Trypetheliaceae, here we present a global species richness estimate for Pyrenulaceae, using a recently devised method based on a global grid system. We refined this approach by using an iterative adjustment to estimate mean predicted grid range per species from a grid frequency histogram. We also adjusted a previously implemented randomization approach to estimate error margins. Our results showed a global estimate for Pyrenulaceae of (395–)441(–453) species world-wide, 307 of which are currently known, thus an overall predicted increase of over 40%. This includes 416 known and predicted tropical and 25 known, exclusively temperate species, the latter assumed to remain unchanged. While the robustness of the global prediction depends on accurately setting grid sampling scores, individual predicted grid richness varies according to additional factors such as evolutionary history. In addition to undescribed species contribution to predicted richness, we hypothesize that species delimitation studies in presumably widespread taxa will reveal refined species concepts with narrower ranges, thus further increasing estimated global richness. The comparison of predicted richness values for the three families Graphidaceae, Trypetheliaceae and Pyrenulaceae with regard to their evolutionary ages highlights this rather robust method as a promising tool to circumvent sampling and knowledge bias when assessing speciation and diversification patterns.