Yeasts fall under the kingdom Fungi. They don't need sunlight to grow. There are two major classifications of yeasts and they are the Saccharomycotina (true yeasts) and the Taphrinomycotina Schizosaccharomycetes (fission yeasts). Most yeast are single-celled, but they sometimes 'glue'together to form chains and become multi-cellular.

Sac fungi, or Ascomycota, is monophyletic and makes up approximately 75% of all described fungi. It includes most of the fungi that combine with algae to form lichens, and the majority of the fungi that lack morphological evidence of sexual reproduction.