(sac fungi) A subdivision of the * Eumycota , most of whose members have a mycelial septate thallus though some (the yeasts) are unicellular. It contains about 16 500 species in almost 2000 genera. Sexual reproduction is by ascospores, with eight characteristically developing within an ascus. It is divided into the classes: * Hemiascomycetes ; * Plectomycetes ; * Pyrenomycetes ; * Discomycetes ; Laboulbenio-mycetes, which are ectoparasites of arthropods; and *Loculoascomycetes. The sac fungi are often placed in the class Ascomycetes, and divided into the two subclasses Hemiascomycetidae (or Protoascomycetidae) and Euascomyce-tidae. About half the ascomycetes have developed a special mode of nutrition in which algal cells are incorporated in the thallus (see lichen ). |
