Muribasidiospora:: Microstromatales or Exobasidiales?

Characteristics of hyphal septation, cellular interaction, sporulation, cultures and/or nuclectide sequences from the 5 ' terminal domain of the nuclear large subunit rRNA gene of some species of Exobasidium, Microstroma and Muribasidiospora were examined and compared. Our analyses show that the order Microstromatales comprises Microstroma, Muribasidiospora triumfetticola and the anamorphic species Rhodotorula bacarum, R. phylloplana and Sympodiomycopsis paphiopedili, whereas Muribasidiospora hesperidium and Muribasidiospora indica are members of the Exobasidiales. Because of the high degree of morphological divergence between Muribasidiospora triumfetticola and Microstroma, a new genus, Volvocisporium, and a new family, Volvocisporiaceac, of the Microstromatales are proposed. Apart from the phylogenetic implications, the most interesting observations in the present work are the unusual development of the basidia, especially of the basidiospores, and the nutrient transport system hom the host attacking hyphae to the basidia in Muribasidiospora triumfetticola.