Taxonomy and phylogeny of the basidiomycetous hyphomycete genus Hormomyces

The taxonomy of the genus Hormomyces, typified by Hormomyces aurantiacus, which based on circumstantial evidence was long assumed to be the hyphomycetous asexual morph of Tremella mesenterica (Tremellales, Tremellomycetes) or occasionally Dacrymyces (Dacrymycetales, Dacrymycetes), is revised. Phylogenies based on the three nuc rDNA markers [internal transcribed spacers (ITS), 28S large ribosomal subunit nrDNA (28S) and 18S small ribosomal subunit nrDNA (18S)], based on cultures from Canada and the United States, suggest that the genus is synonymous with Tulasnella (Cantharellales, Agaricomycetes) rather than Tremella or Dacrymyces. Morphological studies of 38 fungarium specimens of Hormomyces, including the type specimens of H. callorioides, H. fragiformis, H. paridiphilus and H. peniophorae and examination of the protologues of H. abieticola, H. aurantiacus and H. pezizoideus suggest that H. callorioides and H. fragiformis are conspecific with H. aurantiacus while the remaining species are unlikely to be related to Tulasnella. The conidial chains produced by H. aurantiacus are similar to monilioid cells of asexual morphs of Tulasnella species formerly referred to the genus Epulorhiza. The new combination Tulasnella aurantiaca is proposed and the species is redescribed, illustrated and compared with similar fungi. The ecological niche of T. aurantiaca and its possible relationship to orchid root endophytes is discussed. A key to asexual genera with similar conidium ontogeny to T. aurantiaca is provided. Citation: Mack J, Assabgui RA, Seifert KA (2021). Taxonomy and phylogeny of the basidiomycetous hyphomycete genus Hormomyces. Fungal Systematics and Evolution 7: 177–196. doi: 10.3114/fuse.2021.07.09