<e1>Muribasidiospora: Microstromatales</e1> or <e1>Exobasidiales</e1>?<fnr rid="fn1"> <fn id="fn1">Part 188 in the series <e1>Studies in Heterobasidiomycetes</e1> from the Botanical Institute, University of Tübingen.</fn>

Characteristics of hyphal septation, cellular interaction, sporulation, cultures and/or nucleotide sequences from the 5' terminal domain of the nuclear large subunit rRNA gene of some species of <e1>Exobasidium</e1>, <e1>Microstroma</e1> and <e1>Muribasidiospora</e1> were examined and compared. Our analyses show that the order <e1>Microstromatales</e1> comprises <e1>Microstroma</e1>, <e1>Muribasidiospora triumfetticola</e1> and the anamorphic species <e1>Rhodotorula bacarum</e1>, <e1>R. phylloplana</e1> and <e1>Sympodiomycopsis paphiopedili</e1>, whereas<e1> Muribasidiospora hesperidium</e1> and <e1>Muribasidiospora indica</e1> are members of the <e1>Exobasidiales</e1>. Because of the high degree of morphological divergence between <e1>Muribasidiospora triumfetticola</e1> and <e1>Microstroma</e1>, a new genus, <e1>Volvocisporium</e1>, and a new family, <e1>Volvocisporiaceae</e1>, of the <e1>Microstromatales</e1> 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 from the host attacking hyphae to the basidia in <e1>Muribasidiospora triumfetticola</e1>.