Complex patterns of speciation in cosmopolitan “rock posy” lichens - Discovering and delimiting cryptic fungal species in the lichen-forming Rhizoplaca melanophthalma species-complex (Lecanoraceae, Ascomycota)

A growing body of evidence indicates that in some cases morphology-based species circumscription of lichenized fungi misrepresents the number of existing species. The cosmopolitan “rock posy” lichen (Rhizoplaca melanophthalma) species-complex includes a number of morphologically distinct species that are both geographically and ecologically widespread, providing a model system to evaluate speciation in lichen-forming ascomycetes. In this study, we assembled multiple lines of evidence from nuclear DNA sequence data, morphology, and biochemistry for species delimitation in the R. melanophthalma species-complex. We identify a total of ten candidate species in this study, four of which were previously recognized as distinct taxa and six previously unrecognized lineages found within what has been thus far considered a single species. Candidate species are supported using inferences from multiple empirical operational criteria. Multiple instances of sympatry support the view that these lineages merit recognition as distinct taxa. Generally, we found little corroboration between morphological and chemical characters, and previously unidentified lineages were morphologically polymorphic. However, secondary metabolite data supported one cryptic saxicolous lineage, characterized by orsellinic-derived gyrophoric and lecanoric acids, which we consider to be taxonomically significant. Our study of the R. melanophthalma species-complex indicates that the genus Rhizoplaca, as presently circumscribed, is more diverse in western North American than originally perceived, and we present our analyses as a working example of species delimitation in morphologically cryptic and recently diverged lichenized fungi.

Graphical abstractDownload full-size imageHighlights► Molecular data reveal cryptic lineages within the R. melanophthalma species complex. ► Most lineages were morphologically and chemically polymorphic. ► Cryptic lineages exhibit extensive microsympatry without detectable gene flow or hybridization. ► This study indicates overall diversity within umbilicate Rhizoplaca species is vastly underestimated.