The terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota.
Fungi are classified primarily based on the structures associated with sexual reproduction, which tend to be evolutionarily conserved. However, many fungi reproduce only asexually, and cannot be easily placed in a classification based on sexual characters; some produce both asexual and sexual states. These problematic species are often members of the Ascomycota, but may also belong to the Basidiomycota. Even among fungi that reproduce both sexually and asexually, often only one method of reproduction can be observed at a specific point in time or under specific conditions. Additionally, fungi typically grow in mixed colonies and sporulate amongst each other. These facts have made it very difficult to link the various states of the same fungus. At present, Article 59 of the International Code of Botanical Nomenclature permits mycologists to give asexually reproducing fungi (anamorphs) separate names from their sexual states (teleomorphs)[1] but this practice will be discontinued as of January 1, 2013.[2] When names are available for both anamorph and teleomorph states of the same fungus, the holomorph either takes the teleomorph name, or it can under some circumstances take the anamorph name if it is subsequently epitypified with a teleomorph.
Fungi that are not known to produce a teleomorph were historically placed into an artificial phylum, the "Deuteromycota", also known as "Fungi Imperfecti", simply for convenience. Some workers hold that this is an obsolete concept, and that molecular phylogeny allows accurate placement of species which are only known from part of their life cycle. Others retain the term deuteromycetes, but give it a lowercase "d" and no taxonomic rank.[3]
The dual naming system can be confusing for novices. It is essential for workers in plant pathology, mold identification, medical mycology, and food microbiology, fields in which asexually reproducing fungi are commonly encountered.
The 1995 edition of the influential Ainsworth and Bisby’s Dictionary of the Fungi sought to replace the term anamorph with mitosporic fungus and teleomorph with meiosporic fungus, based on the idea that the fundamental distinction is whether mitosis or meiosis preceded sporulation. This is a controversial choice because it is not clear that the morphological differences which traditionally define anamorphs and teleomorphs line up completely with sexual practices, or whether those sexual practices are sufficiently well understood in some cases.[3]
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