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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 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, Volvocisporiaceae , 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 from the host attacking hyphae to the basidia in Muribasidiospora triumfetticola.

Evidence is presented to show that the fungus, originally described as a species of Cercosporella (Hyphomycetes), introduced into Hawaii to control the composite weed Ageratina riparia, belongs to the white smuts (Ustilaginales). It is formally described as Entyloma ageratinae sp. nov. In addition to two external spore types (sporidia), which occur in prominent hypophyllous caespituli, hyaline, thin-walled, non-resting ustilospores are formed within non-necrotic leaf tissue. A further spore type, the spermatium, is abundantly produced from well-defined spermogonia. The significance of these previously unreported structures in the smut life-cycle is discussed. Entyloma ageratinae was found to be present in the purported centre of origin of its weed host, the Jalapa (Vera Cruz) region of Mexico. Further collections of white smuts on other composite weeds (Parthenium hysterophorus, Melampodium divaricatum) in this locality are assigned to E. compositarum and compared with E. ageratinae. The additional discovery of Kordyana cubensis (Exobasidiales) on Commelina diffusa with a similar spermogonial state is reported and discussed in relation to the evolution of the Ustilaginales and Exobasidiales.