The expanding realm of ballistosporous yeasts.

The recent progress in the systematics of ballistosporous yeasts is discussed. The extensive isolation studies carried out in the last decade resulted in a marked increase in the number of ballistosporous yeast species which now number nearly fifty. The increased number of species has expanded the complexity of taxonomic properties in the following ways: expansion of the range of mol% G+C of nuclear DNA to 39-68.5, thus overlapping that of all basidiomycetous yeasts; increased complexity of conidiogenesis with the finding of the genera Ballistosporomyces and Kockovaella. Based on partial sequencing of 18S ribosomal RNA (positions 1451-1618 in Saccharomyces cerevisiae), it is suggested that mode of conidiogenesis has little value for defining genera. Consequently, ballistosporous yeasts merely represent the "ballistosporous stage" of various taxa which cover the whole evolutionary spectrum of basidiomycetous yeasts. The importance of continuing isolation of ballistosporous yeasts is stressed, which together with molecular studies, will aid further progress in the systematics of basidiomycetous yeasts.