<i>Cladosterigma</i>: an enigmatic fungus, previously considered a basidiomycete, now revealed as an ascomycete member of the Gomphillaceae

<i>Cladosterigma clavariellum</i> has been treated as a basidiomycete since its first description by Spegazzini in 1886 as <i>Microcera clavariella</i>. After further morphological studies, between 1919 and 2011, it remained among the basidiomycetes, most recently as incertae sedis in the order Cryptobasidiales. Our studies, based on light and scanning electron microscopy, supported by multilocus phylogenetic analyses—second-largest subunit of RNA polymerase II (<i>RPB2</i>), translation elongation factor 1-alpha (<i>TEF1</i>), small subunit (18S), large subunit (28S), and nuclear internal transcribed spacers (ITS1-5.8S-ITS2 = ITS) of the nuclear rDNA sequences, and mitochondrial rDNA small subunit (mtSSU)—finally determined the phylogenetic placement of <i>Cladosterigma</i> as the first nonlichenicolous mycoparasitic member of the Gomphillaceae within the Graphidales, an ascomycete order previously composed predominantly of lichen-forming fungi.