An order of the *Hemiascomycetes
containing about 200 species in some 50 genera. It includes the family Saccharomycetaceae, the yeasts, which contains the commercially important species Saccharomyces cerevisiae (brewer's yeast), used in bread and beer making, and S. ellipsoideus, used in wine making. The yeasts reproduce asex-ually by budding or by dividing into two equal cells as in Schizosaccharomyces (fission yeasts). Sexual reproduction is by ascus formation.