A Discussion on the Genus Stigmatomyces Sensu Lato and the Description of Two New Species from Chile

Taxonomic revisions in mycology often focus on well-studied fungal groups, yet obscure lineages such as Laboulbeniales (Pezizomycotina, Ascomycota) remain underexplored. Here, we address the taxonomy of Stigmatomyces sensu lato, a diverse genus of obligate biotrophic fungi parasitizing flies (Diptera). Previous work suggested that Stigmatomyces is paraphyletic, as the well-delineated genus Gloeandromyces was nested within the genus, which resulted in the reinstatement of Appendiculina and Fanniomyces. We reconstructed a molecular phylogeny of Stigmatomyces sensu lato using three genetic markers (18S and 28S nuc rDNA, TEF1α) and significantly expanded taxon sampling. Our results recovered six well-supported clades, including the three aforementioned genera, Stigmatomyces sensu stricto, and two unnamed lineages. Although the internal relationships among these clades remain unresolved, morphological distinctions further support their delimitation. We provide arguments both for and against splitting of the genus. A formal split of Stigmatomyces is not proposed due to still limited data and especially the lack of sequences from the type species, S. baeri. However, our findings are in support of the splitting of Stigmatomyces sensu lato in the future. Based on molecular phylogenetic, morphological, and ecological data, we also describe two new species from Chile, Appendiculina drosophilae-huillicheae on Drosophila huilliche (Drosophilidae) and Stigmatomyces beukii on Prosopantrum sp. (Cnemospathididae). Based on morphological, ecological, and/or molecular phylogenetic data, we propose four new combinations: Appendiculina dacina, A. majewskii, Bordea euconni, and Sphaleromyces montevideensis. Finally, we validly publish Stigmatomyces biformis and propose Stigmatomyces rakiurensis to accommodate S. australis M.B. Hughes, A. Weir, Gillen & W. Rossi, a later homonym of S. australis Thaxt.