A group of fungi consisting of yeasts that reproduce asexually by budding or splitting of single cells. In spite of simple morphology, these yeasts are quite diverse in terms of evolutionary origins and environmental roles. The group contains the yeasts used in baking and brewing. Some other yeasts are responsible for infections in humans and animals, while others occur on leaves or fruits. A few species are used for biological control of microbial plant pathogens. A very small number are pathogens of plants.