Members of the Division Ascomycota are known as the Sac Fungi and are fungi that produce spores in a distinctive type of microscopic sporangium called an ascus (Greek for a "bag" or "wineskin"). This monophyletic grouping was formerly known as the Ascomycetae and is an extremely significant and successful group of organisms (12,000 species in 1950), accounting for some 75% of all described fungi. Included are most of the fungi that combine with algae to form lichens. The majority of fungi that lack morphological evidence of sexual reproduction are placed here. Better known examples of sac fungi are yeasts, morels, truffles, and Penicillium. The majority of plant-pathogenic fungi belong to this group, or the related Deuteromycota. Species of ascomycetes are also popular in the laboratory. Sordaria fimicola, Neurospora crassa and several species of yeasts are used in many genetics and cell biology experiments.

An ascomycete produces great numbers of asci at any one time, and these may be contained in a structure called an ascocarp. Each ascus contains eight (or a multiple of 8) ascospores, the result of one round of mitosis following meiosis. The resulting haploid nuclei are surrounded by membranes (from the plasma membrane in Euascomycetes; from the nuclear membrane in Hemiascomycetes) and eventually a spore wall.

An exception to the structure described above are the yeasts, which are secondarily unicellular.

External links

• Tree of Life Web Project: Ascomycota (http://tolweb.org/tree?group=Ascomycota&contgroup=Fungi)