The term “yeast” does not refer to any recognized taxonomic name but instead describes fungi that are unicellular and usually reproduce asexually by budding. The term yeast is also used, more specifically, for those species in the genus Saccharomyces that are used to leaven bread and ferment alcoholic beverages.
Among mycologists, there is some disagreement over what should be called a yeast. Many mycologists use the term to describe any fungus that has a unicellular budding format any time in its life. They often use the term “monomorphic” to describe those that are always unicellular and the term “dimorphic” to describe those that can have both unicellular and filamentous growth.
Others, however, reserve the name yeast for those species that are permanently unicellular and use the term “yeastlike” to describe those fungi that can alternate between mycelial and unicellular forms. Because some species that have traditionally been called yeasts have later been shown to have a mycelial form, the former broader definition will be used here.
