Hidden diversity in the morphologically variable script lichen (Graphis scripta) complex (Ascomycota, Ostropales, Graphidaceae)

Abstract

Graphis scripta, or script lichen, is a well-known species of crustose lichenized fungi, widely distributed in the temperate region of the Northern Hemisphere. It is now considered to be a species complex, but because of the lack of secondary chemistry and paucity of measurable morphological characters, species delimitation within the complex has been challenging and is thus far based on apothecium and ascospore morphology. In this study, we employed molecular as well as morphological data to assess phylogenetic structure and delimitation of lineages within the G. scripta complex. We generated sequences for four genetic markers (mtSSU, nuLSU, RPB2, and EF-1) and performed phylogenetic analyses. The resulting trees were used to determine the number of distinct lineages by applying a general mixed Yule-coalescent (GMYC) model and species tree estimation through maximum likelihood (STEM). Our analyses suggest between six and seven putative species within the G. scripta complex. However, these did not correspond to the taxa that were recently distinguished based on apothecium morphology and could not be circumscribed with the morphological characters that were traditionally used in the classification of the complex. Any formal taxonomic treatment will require additional sampling and evaluation of additional traits that potentially can characterize these clades.