Teleomorph, anamorph and holomorph

This article is about life cycles of fungi. For other uses see Anamorph (disambiguation)

In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota.

Dual naming of fungi

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 a few of them 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.

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.[1]

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.

Historically, Article 59 of the International Code of Botanical Nomenclature permitted mycologists to give asexually reproducing fungi (anamorphs) separate names from their sexual states (teleomorphs)[2] but this practice was discontinued as of 1 January 2013.[3]

From dual system to single nomenclature

The concept of permitting separate names for anamorphs of fungi with a pleomorphic life-cycle has been an issue of debate since the phenomenon was recognized in the mid-19th century.[3] This was even before the first international rules for "botanical" nomenclature were issued in 1867.[3] Special provisions are to be found in the earliest Codes, which were then modified several times, and often substantially.[3] The rules became increasingly complex, and by the mid-1970s they were being interpreted in different ways by different mycologists – even ones working on the same genus.[3] Following intensive discussions under the auspices of the International Mycological Association, drastic changes were made at the Sydney Congress in 1981 to clarify and simplify the procedures – and the now familiar terms anamorph, teleomorph, and holomorph entered general use.[3] An unfortunate effect of the simplification was that many name changes had to be made as a consequence, including ones of some well-known and economically important species; at that date, the conservation of species names was not allowed under the Code.[3]

Unforeseen in the 1970s, when the 1981 provisions were crafted, was the impact of molecular systematics.[3] A decade later, it was starting to become obvious that fungi with no known sexual stage could confidently be placed in genera which were typified by species in which the sexual stage was known, and the issue of the abandonment of the dual nomenclatural system was posited.[3] This possibility was debated at subsequent International Mycological Congresses, and on other occasions, and the need for change was increasingly recognized.[3] Cannon and Kirk (2000)[4] regarded deletion as inevitable in the long-term, and further calls for deleting the provision followed.[3] At the International Botanical Congress in Vienna in 2005, some minor modifications were made which allowed anamorph-typified names to be epitypified by material showing the sexual stage when it was discovered, and for that name or epithet to continue to be used where there was no previously sexually-typified name available.[3]

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.[1]

More importantly, the Vienna Congress established a Special Committee to investigate the issue further, but unfortunately it was unable to reach a consensus.[3] Matters were becoming increasingly desperate as mycologists using molecular phylogenetic approaches started to ignore the provisions, or interpret them in different ways.[3] The view that emerged from the International Mycological Congress in Edinburgh the same year, was that mycologists, as a whole, favoured gradual progress towards a single nomenclature.[3] In the meantime, various proposals were made to improve the situation, but the situation was becoming so complex that few mycologists were likely to take the time to understand them fully and implement them correctly.[3] In order to progress the matter, an international symposium was held in Amsterdam in April 2011, under the auspices of the International Commission on the Taxonomy of Fungi, to explore ways to obtain a solution.[3] If a solution could not be reached at the Melbourne Congress, the prospect was for no substantive change to be made until after the 2017 International Botanical Congress.[3] This situation would then have become intolerable as mycologists increasingly ignore the rules.[3]

The Amsterdam symposium prepared a declaration of principles which, it was hoped, would be accommodated in any change made to Article 59.[3] In effect these amounted to the ending of dual nomenclature, but with safeguards to minimize changes in familiar names.[3] The "Amsterdam Declaration" prompted a critical response from some other mycologists who perceived difficulties in aspects of the declaration, and wished to continue allowing dual nomenclature.[3] Both these documents were made available to delegates at the Melbourne Congress.[3] In order to ensure some resolution of the issue, proposals for three possible options were developed by Redhead, in consultation with various mycologists, for presentation at the meeting.[3] Following extensive discussions at the Congress, the option to discontinue the dual nomenclature system was approved, but with some safeguards to limit resultant instability.[3]

One fungus, one name

The International Botanical Congress in Melbourne in July 2011 made a change in the International Code of Nomenclature for algae, fungi, and plants and adopted the principle "one fungus, one name".[3]

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.

After 1 January 2013, one fungus can only have one name; the system of permitting separate names to be used for anamorphs then ended.[3] This means that all legitimate names proposed for a species, regardless of what stage they are typified by, can serve as the correct name for that species.[3] All names now compete on an equal footing for priority regardless of the stage represented by the name-bearing type.[3] In order not to render names that had been introduced in the past for separate morphs as illegitimate, it was agreed that these should not be treated as superfluous alternative names in the sense of the Code.[3] It was further decided that anamorph-typified names should not be taken up to displace widely used teleomorph-typified names until the case has been considered by the General Committee established by the Congress.[3] Recognizing that there were cases in some groups of fungi where there could be many names that might merit formal retention or rejection, a new provision was introduced.[3] It was decided that lists of names can be submitted to the General Committee and, after due scrutiny, names accepted on those lists are to be treated as conserved over competing synonyms (and listed as Appendices to the Code).[3] Lichen-forming fungi (but not lichenicolous fungi) had always been excluded from the provisions permitting dual nomenclature; the new Code will include a paragraph to make it explicit that lichen-forming fungi are excluded from the newly accepted provisions.[3]

See also

References

This article incorporates CC-BY-3.0 text from the reference[3]

  1. ↑ 1.0 1.1 Guarro, J; Genéj; Stchigel, Am (Jul 1999), "Developments in fungal taxonomy" (Free full text), Clinical Microbiology Reviews 12 (3): 454–500, ISSN 0893-8512, PMC 100249, PMID 10398676
  2. ↑ Article 59 of the International Code of Botanical Nomenclature
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34 Hawksworth, D. L. (2011). "A new dawn for the naming of fungi: impacts of decisions made in Melbourne in July 2011 on the future publication and regulation of fungal names". MycoKeys 1: 7–20. doi:10.3897/mycokeys.1.2062.
  4. ↑ Cannon, P. F.; Kirk, P. M. (2000). "The philosophies and practicalities of amalgamating anamorph and teleomorph concepts". Studies in Mycology 45: 19–25.

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