Comparisons of sequences of the ribosomal gene (partial SSU-ITS-partial LSU) of members of some species clades of the recently created family Septoglomeraceae (arbuscular mycorrhizal fungi (AMF) of the phylum Glomeromycota) showed that, molecularly, these clades are diverged by about 10% in terms of maximum identity (MI). In the order Glomerales of the phylum, such divergences generally occur between taxa at the rank of genus. Therefore, the aim of the present study was to verify the phylogenies of members of Septoglomeraceae and their morphological characters. These verifications showed that Septoglomus titan and Viscospora peruviscosa should represent two autonomous single-species clades. Consequently, S. titan was assigned to the genus, Melanoglomus gen. nov., with Me. titan comb. nov. The main morphological differences between Me. titan and the other Septoglomus species lie in the structure of the spore wall and the phenotypic properties of its components. Viscospora peruviscosa was transferred to a new genus, Microviscospora, with Mi. peruviscosa comb. nov., whose spores are much smaller than those of V. viscosa, currently the only member of the genus Viscospora. Melanoglomus titan and Mi. peruviscosa probably represent two rare AMF species, which have so far been found only in Brazil, Peru, and Saudi Arabia, respectively. Furthermore, our morphological and phylogenetic analysis using specimen-based sequences support Blaszkowskia as an autonomous genus-clade in Septoglomeraceae. Currently, Septoglomeraceae comprises seven genera: Blaszkowskia, Funneliformis, Funneliglomus, Melanoglomus, Microviscospora, Septoglomus, and Viscospora, and Glomerales includes 26 genera. An updated morphological key for the identification of genera of Glomerales is included.
