EVOLUTIONARY RELATIONSHIPS AMONG HIGHER FUNGI INFERRED FROM SMALL RIBOSOMAL-SUBUNIT RNA SEQUENCE-ANALYSIS

The primary structure of the small ribosomal subunit RNA. (SSU rRNA) w as determined for 13 species belonging to 10 ascomycete families and f or the basidiomycetous anamorphic yeast Rhodotorula glutinis. The sequ ences were fitted into an alignment of all hitherto published complete or nearly complete eukaryotic small subunit rRNA sequences. The evolu tionary relationships within the fungi were examined by construction o f a tree from 87 SSU rRNA sequences, corresponding to 71 different spe cies, by means of a distance matrix method and bootstrap analysis. It confirms the early divergence of the zygomycetes and the classical div ision of the higher fungi into basidiomycetes and ascomycetes. The bas idiomycetes are divided into true basidiomycetes and ustomycetes. With in the ascomycetes, the major subdivisions hemiascomycetes and euascom ycetes can be recognized. However, Schizosaccharomyces pombe does not belong to the cluster of the hemiascomycetes, to which it is assigned in classical taxonomic schemes, but forms a distinct lineage. Among th e euascomycetes, the plectomycetes and the pyrenomycetes can be distin guished. Within the hemiascomycetes, the polyphyly of genera like Pich ia or Candida and of families like the Dipodascaceae and the Saccharom ycetaceae can be observed.