Synonomy of the yeast genera Hansenula and Pichia demonstrated through comparisons of deoxyribonucleic acid relatedness.

The relationship between the genera Hansenula and Pichia was examined through comparisons of DNA relatedness among phenotypically similar species. Hansenula minuta and Pichia lindneri showed 75% DNA base sequence complementarity. In other comparisons, H. nonfermentans was found to share nearly 50% of its DNA sequences with both H. minuta and P. lindneri. Because of the high degree of relatedness observed, it is proposed that ability to assimilate nitrate, the sole distinction between Hansenula and Pichia, is of insufficient taxonomic value for the reliable separation of either species or genera. Hat-spored species of Hansenula H. et P. Sydow 1919 are being transferred to Pichia Hansen 1904. Species of Hansenula and Pichia with Saturn-shaped ascospores will be transferred to the genus Williopsis.