Six polymorphic yeast strains with strong antifungal activities isolated from dicot plants in an alkaline-lake desert region were subjected to taxonomic examination. The phylogenetic trees reconstructed by using neighbour-joining, maximum-likelihood and Bayesian methods from concatenated D1/D2 and ITS-5.8S-ITS2 sequences revealed phylogenetic affinity to Ustilaginaceae, but the large phylogenetic distance separating the isolates from the most closely related groups of species indicates that they represent a separate species. The sequences of the genes coding for the LSU rDNA, act1, rpb2 and a protein of unknown function corroborate this position. The isolates can easily be distinguished from their closest relatives by physiological tests (utilisation of carbon and nitrogen sources). Based on these results, a new species,