Ascomycota(redirected from ascomycetous)
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Related to ascomycetous: Ascomycota, Sac fungi
Ascomycota,a phylum of the kingdom FungiFungi
, kingdom of heterotrophic single-celled, multinucleated, or multicellular organisms, including yeasts, molds, and mushrooms. The organisms live as parasites, symbionts, or saprobes (see saprophyte).
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A phylum in the kingdom Fungi, representing the largest of the major groups of fungi, and distinguished by the presence of the ascus, a specialized saclike cell in which fusion of nuclei and reduction division occur and the resulting nuclei form ascospores. In most ascomycetes, each ascus contains eight ascospores, but the number may vary from one to several hundred. In the simplest ascomycetes (yeasts), the vegetative body (thallus) is unicellular; however, in the majority of ascomycetes, the thallus is more complex and consists of a tubular, threadlike hypha with cross walls which grows in or on the substrate. These hyphae eventually form structures called ascomata (ascocarps), on or in which the asci are formed. In addition to their sexual reproduction, most ascomycetes reproduce asexually by means of conidia.
Traditionally, the structure of the ascoma and ascus has served as the basis for subdividing the Ascomycota into five classes: Hemiascomycetes, Plectomycetes, Pyrenomycetes, Discomycetes, Loculoascomycetes. The introduction of molecular data, however, is changing concepts of the relationships of different groups of ascomycetes and will eventually lead to a much-revised classification scheme.
The ascomycetes occur throughout the world in all types of habitats and on both living and dead substrates. An estimated 33,000 species are arranged in about 3300 genera, with new species being described regularly. Ecologically ascomycetes function as primary decomposers of plant materials, but they also are important as plant and human pathogens; in baking, brewing, and winemaking; in enzyme and acid production; and as sources of antibiotics and other drugs. See Eumycota, Fungi, Plant pathology, Yeast