A Scytalidium-like indoor fungus revealing polyphyletic relationships and convergent evolution in Scytalidium

A Scytalidium-like fungus was isolated from a dust sample collected indoors in the USA. Partial DNA sequences for the genomic regions of the 5.8S nuclear ribosomal DNA and flanking internal transcribed spacer (ITS), the nuclear ribosomal large subunit (LSU), the translation elongation factor 1-α (tef1), the β-tubulin (tub2) and the DNA-directed RNA polymerase II second largest subunit (rpb2) genes were determined. Phylogenetic analyses indicated that the indoor Scytalidium-like fungus is closely related to Scytalidium flavobrunneum, yet neither fungus is phylogenetically related to the generic type species, Scytalidium lignicola. Further analyses revealed that members of Scytalidium are polyphyletic belonging to eight orders: Amphisphaeriales, Coryneliales, Helotiales, Hypocreales, Mycosphaerellales, Pleosporales, Sordariales, Xylariales; seven subclasses: Coryneliomycetidae, Dothideomycetidae, Hypocreomycetidae, Leotiomycetidae, Pleosporomycetidae, Sordariomycetidae, Xylariomycetidae and four classes: Eurotiomycetes, Dothideomycetes, Leotiomycetes, and Sordariomycetes. Scytalidium s.s. belongs to Helotiales. The indoor fungus has dimorphic anamorphs and belongs to Monochaetia, Amphisphaeriales using sequences of five loci (ITS, LSU, tub2, tef1 and rpb2). Species of Scytalidium belonging to other orders are combined in their respective genera based on phylogenetic analyses using ITS and LSU. In our opinion, the polyphyletic nature of Scytalidium-like fungi shared morphological characteristics is the result of convergent evolution. At the same time, three new species, Scytalidium ruthenicum D.W. Li & N.P. Schultes, Monochaetia domiciliana D.W. Li & N.P. Schultes and Monochaetia arboricola D.W. Li & N.P. Schultes, were described and illustrated.