Deuteromycota

The Deuteromycota (Greek for "second fungi") were once considered a formal phylum of the kingdom Fungi. The term is now used only informally, to denote species of fungi that are asexually reproducing members of the fungal phyla Ascomycota and Basidiomycota.

Other names for the Deuteromycota have included Deuteromycetes and Fungi imperfecti. Currently these fungi are most often called anamorphic fungi, or mitosporic fungi, but these are informal terms without taxonomic rank.

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Problems in taxonomic classification

Although the taxon Deuteromycota is no longer formally accepted, many of the fungi it included have yet to find a place in modern fungal classification. This is because most fungi are classified based on characteristics of the fruiting bodies and spores produced during sexual reproduction, but members of the Deuteromycota have only been observed to produce asexual spores.

For this reason, mycologists are unique among those who study extant organisms in using a dual system of nomenclature. Dual naming is permitted by Article 59 of the International Code of Botanical Nomenclature (which governs the naming of plants and fungi). Under this system, a name for an asexually reproducing fungus is considered a 'form taxon.' For example, the ubiquitous and industrially important mold, Aspergillus niger, has no known sexual cycle. Thus Aspergillus niger is considered a form taxon. In contrast, the sexual state of its close relative Aspergillus nidulans was found to be Emericella nidulans. When a teleomorph is known, its name takes priority over the name of the anamorph, hence the latter fungus is properly called Emericella nidulans.

Phylogeny and taxonomy

Common approaches of phylogenetic classification of asexually reproducing fungi now include the methods of molecular systematics. The resulting phylogenetic trees based on DNA sequences, such as rDNA, or multigene phylogenies can be used to test hypotheses regarding the relationships among asexually reproducing fungi and to their sexually reproducing counterparts. In this way, many asexually reproducing fungi have found their place in the tree of life.^{[citation needed]} However, this approach requires a significant investment of time and resources, and can often not be applied to fungal species that are not available as cultures or fresh specimens. Furthermore, under the current system of fungal nomenclature, teleomorph names cannot be applied to fungi that lack sexual structures. Classifying and naming asexually reproducing fungi is the subject of ongoing debate in the mycological community.

Historical classification of the Deuteromycota

These groups are no longer formally accepted because they do not adhere to the principle of monophyly. The taxon names are sometimes used informally. In particular, the term 'hyphomycetes' is often used to refer to molds, and the term 'coelomycetes' is used to refer to many asexually reproduing plant pathogens that form discrete fruiting bodies. Other systems of classification are reviewed by Kendrick (1981)^[1].

• Class Hyphomycetes lacking fruiting bodies
  • Order Moniliales (producing spores on simple conidiophores)
  • Order Stilbeliales(producing spores on synemmata)
  • Order Tuberculariales (producing spores in sporodochia)

• Class Coelomycetes spores produced in fruiting bodies
  • Order Melanconiales (producing spores in acervuli)
  • Order Sphaeropsidales (producing spores in pycnidia)

• Class Agonomycetales lacking spores

References

Gams, W. 1995. How natural should anamorph genera be? Canadian Journal of Botany 73 (suppl 1):S747-S753.

Kendrick, B. 1981. The history of conidial fungi, Pages 3-18 in GT Cole and B Kendrick, eds. Biology of Conidial Fungi. New York, Academic Press.

Seifert, KA. 1993. Integrating anamorphic fungi into the fungal system, Pages 79-85 in DR Reynolds, and JW Taylor, eds. The Fungal Holomorph: mitotic, meiotic and pleomorphic speciation in fungal systematics. Wallingford, UK, CAB International.

Taylor, JW. 1995. Making the Deuteromycota redundant: a practical integration of mitosporic and meiosporic fungi. Canadian Journal of Botany 73 (suppl 1):S754-S759.