Heterobasidiomycetes

Last updated November 15, 2023

Heterobasidiomycetes, including jelly fungi, smuts and rusts, are basidiomycetes with septate basidia. This contrasts them to homobasidiomycetes (alternatively called holobasidiomycetes), including most mushrooms and other Agaricomycetes, which have aseptate basidia. The division of all basidiomycetes between these two groups has been influential in fungal taxonomy,^[1] and is still used informally, but it is no longer the basis of formal classification. In modern taxonomy^[2] homobasidiomycetes roughly correspond to the monophyletic class Agaricomycetes, whereas heterobasidiomycetes are paraphyletic and as such correspond to various taxa from different taxonomic ranks, including the Basidiomycota other than Agaricomycetes and a few basal groups within Agaricomycetes.

Distinction between homo- and heterobasidiomycetes

In addition to having septate basidia, heterobasidiomycetes also frequently possess large irregularly shaped sterigmata and spores that are capable of self-replication – a process where a spore, instead of germinating into a vegetative hypha, gives rise to a sterigma and a new spore, which is then discharged as if from a normal basidium. In contrast, homobasidiomycetes, in addition to having aseptate basidia, generally have small regularly shaped sterigmata and spores that do not self-replicate. In different classifications, different features have been stressed.^[1]

Intermediate forms

Certain taxa, such as Dacrymycetaceae, Ceratobasidiaceae or Tulasnellaceae, due to possessing a combination of hetero- as well as homobasidiomycetous features, have been difficult to definitively assign to either group, resulting in dissenting opinions among taxonomists.^[3] For example, Dacrymycetaceae possess very large and irregularly shaped sterigmata as well as self-replicating spores, but have aseptate basidia. Tulasnellaceae have self-replicating spores and grossly swollen sterigmata that are separated from the basidium with a septum at the base, however the basidial body itself is not septate and the sterigmata and the basidium are quite regularly shaped. Ceratobasidiaceae have aseptate basidia, but the sterigmata are quite large and irregular and the spores are self-replicating.

History

The terms homo- and heterobasidiomycetes were coined by Patouillard in 1900 ("Hétérobasidiés" and "Homobasidiés").^[4] He divided all basidiomycetes between these two groups. This distinction formed the basis of various classifications up to the end of the 20th century.^[1] The terms have been used for taxa at the subclass but later at the class level, as fungi were elevated from a phylum of plants to an independent kingdom (consequently shifting the class Basidiomycetes to the phylum Basidiomycota).

Homobasidiomycetes have been present in most if not all major classifications throughout the 20th century (called holobasidiomycetes in some), and only vary with regard to which of the groups combining both hetero- and homobasidiomycetous features are included.^[1] The composition of Heterobasidiomycetes has been more variable.^[1] In addition to the variable inclusion or exclusion of groups with intermediate features, they have frequently been split into two different groups alongside homobasidiomycetes (one including either only smuts or both smuts and rusts, and the other including the remaining heterobasidiomycetes, mainly jelly fungi). Toward the end of the 20th century, the term "heterobasidiomycetes" has sometimes been reserved to jelly fung only, excluding smuts and rusts.^[5]

Throughout most of the 20th century, no single one of these systems gained dominance over the others.^[1] In the last quarter of the 20th century, micrography of the septal pore apparatus began to clarify the true phylogenetic relationships in Basidiomycota.^[5] However, it was not until the use of molecular systematics in the 90s and early 2000s that fungal taxonomy arrived at a consensus.^[2]

Brefeld 1987	Patouillard 1900^[4]	Lowy 1968^[3]	Talbot 1968^[6]	Donk 1972^[7]^[8]	Wells 1994^[5]
Protobasidiomycetes (septate basidia) Auricularieae Tremellineae Uredineae (=Pucciniales) Ustilagineae Autobasidiomycetes (aseptate basidia) containing only homobasidiomycetes sensu stricto	Hétérobasidiés (self-replicating spores, septate basidia) Auriculariaceae Caloceraceae (=Dacrymycetaceae) Tremellaceae Tulasnellaceae Homobasidiés (spores not self-replicating, basidia aseptate) containing only homobasidiomycetes sensu stricto	Heterobasidiomycetidae (completely septate basidia) Ustilaginales Uredinales (=Pucciniales) Eutremellales (including Auriculariaceae and Tremellaceae) Metabasidiomycetidae (incompletely septate or aseptate basidia, large swollen sterigmata, self-replicating spores) Metatremellales (including Ceratobasidiaceae, Dacrymycetaceae and Tulasnellaceae) Homobasidiomycetidae (completely aseptate basidia, sterigmata not swollen, spores not self-replicating) containing only homobasidiomycetes sensu stricto	Teliobasidiomycetes (meiotically septate basidia, teliospores) smuts rusts Phragmobasidiomycetes (meiotically septate basidia, no teliospores) auricularioid fungi tremelloid fungi Holobasidiomycetes (basidia not meiotically septate; identical to Donk 1972) containing ceratobasidioid, dacrymycetoid and tulasnelloid fungi in addition to homobasidiomycetes sensu stricto	Hemibasidiomycetes (meiotically septate basidia) smuts Phragmobasidiomycetes (meiotically septate basidia) rusts auricularioid fungi tremelloid fungi Holobasidiomycetes (basidia not meiotically septate; identical to Talbot 1968) containing ceratobasidioid, dacrymycetoid and tulasnelloid fungi in addition to homobasidiomycetes sensu stricto	Teliomycotina (septal pore simple) smuts rusts Basidiomycotina (septal pore complex) Heterobasidiomycetes (basidia septate or if not septate then deeply divided, spores self-replicating) Heterobasidiomycetidae Auriculariales Ceratobasidiales Dacrymycetales Tulasnellales Tremellomycetidae Tremellales Homobasidiomycetes (basidia aseptate, spores not self-replicating) containing only homobasidiomycetes sensu stricto

Modern view

A phylogenetic analysis of nuclear ribosomal genes in 1993^[1] showed that heterobasidiomycetes as originally circumscribed by Patouillard in 1900 in fact correspond quite well to a grade of fungi that is paraphyletic in relation to the homobasidiomycetes, the bulk of the latter forming a monophyletic clade. Remarkably, despite a century long effort, classifications after Patouillard had only increased the distance from the true phylogeny.^[1] The subsequent rapid accumulation of molecular data in the past two decades has allowed mycologists to abandon the use of paraphyletic taxa and arrive at a consensus classification based on monophyletic clades that was finalized in 2007.^[2]

The bulk of homobasidiomycetes forms a monophyletic clade, constituting majority of the modern Agaricomycetes. Heterobasidiomycetes correspond to most Basidiomycota other than the homobasidiomycetes: the subphyla Ustilaginomycotina (smuts), Pucciniomycotina (rusts and a variety of other forms), and from the subphylum Agaricomycotina the classes Tremellomycetes and Dacrymycetes, the orders Auriculariales and Sebacinales within the class Agaricomycetes, and the families Ceratobasidiaceae and Tulasnellaceae from the agaricomycete order Cantharellales (these members of the Agaricomycotina, save for the web-like Ceratobasidiaceae, are collectively known as the jelly fungi).

homobasidiomycetes groups with intermediate features heterobasidiomycetes

Related Research Articles

Basidiomycota is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basidiomycota includes these groups: agarics, puffballs, stinkhorns, bracket fungi, other polypores, jelly fungi, boletes, chanterelles, earth stars, smuts, bunts, rusts, mirror yeasts, and Cryptococcus, the human pathogenic yeast.

A basidium is a microscopic spore-producing structure found on the hymenophore of reproductive bodies of basidiomycete fungi. These bodies also called tertiary mycelia, which are highly coiled versions of secondary mycelia. The presence of basidia is one of the main characteristic features of the genus. A basidium usually bears four sexual spores called basidiospores. Occasionally the number may be two or even eight. Each reproductive spore is produced at the tip of a narrow prong or horn called a sterigma (pl. sterigmata), and is forcefully expelled at full growth.

In fungi, a basidiocarp, basidiome, or basidioma (pl. basidiomata) is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do not produce such structures. As with other sporocarps, epigeous (above-ground) basidiocarps that are visible to the naked eye are commonly referred to as mushrooms, while hypogeous (underground) basidiocarps are usually called false truffles.

A basidiospore is a reproductive spore produced by Basidiomycete fungi, a grouping that includes mushrooms, shelf fungi, rusts, and smuts. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. Typically, four basidiospores develop on appendages from each basidium, of which two are of one strain and the other two of its opposite strain. In gills under a cap of one common species, there exist millions of basidia. Some gilled mushrooms in the order Agaricales have the ability to release billions of spores. The puffball fungus Calvatia gigantea has been calculated to produce about five trillion basidiospores. Most basidiospores are forcibly discharged, and are thus considered ballistospores. These spores serve as the main air dispersal units for the fungi. The spores are released during periods of high humidity and generally have a night-time or pre-dawn peak concentration in the atmosphere.

The Ustilaginomycotina is a subdivision within the division Basidiomycota of the kingdom Fungi. It consists of the classes Ustilaginomycetes and Exobasidiomycetes, and in 2014 the subdivision was reclassified and the two additional classes Malasseziomycetes and Monilielliomycetes added. The name was first published by Doweld in 2001; Bauer and colleagues later published it in 2006 as an isonym. Ustilagomycotina and Agaricomycotina are considered to be sister groups, and they are in turn sister groups to the subdivision Pucciniomycotina.

Dikarya is a subkingdom of Fungi that includes the divisions Ascomycota and Basidiomycota, both of which in general produce dikaryons, may be filamentous or unicellular, but are always without flagella. The Dikarya are most of the so-called "higher fungi", but also include many anamorphic species that would have been classified as molds in historical literature. Phylogenetically the two divisions regularly group together. In a 1998 publication, Thomas Cavalier-Smith referred to this group as the Neomycota.

Pucciniomycotina is a subdivision of fungus within the division Basidiomycota. The subdivision contains 10 classes, 21 orders, and 38 families. Over 8400 species of Pucciniomycotina have been described - more than 8% of all described fungi. The subdivision is considered a sister group to Ustilaginomycotina and Agaricomycotina, which may share the basal lineage of Basidiomycota, although this is uncertain due to low support for placement between the three groups. The group was known as Urediniomycetes until 2006, when it was elevated from a class to a subdivision and named after the largest order in the group, Pucciniales.

Agaricomycotina is one of three subdivisions of the Basidiomycota, and represents all of the fungi which form macroscopic fruiting bodies. Agaricomycotina contains over 30,000 species, divided into three classes: Tremellomycetes, Dacrymycetes, and Agaricomycetes. Around 98% of the species are in the class Agaricomycetes, including all the agarics, bracket fungi, clavarioid fungi, corticioid fungi, and gasteroid fungi. Tremellomycetes contains many basidiomycete yeasts and some conspicuous jelly fungi. Dacrymycetes contains a further group of jelly fungi. These taxa are founded on molecular research, based on cladistic analysis of DNA sequences, and supersede earlier morphology-based classifications. Agaricomycotina contains nearly one third of all described species of fungi.

The Auriculariales are an order of fungi in the class Agaricomycetes. Species within the order were formerly referred to the "heterobasidiomycetes" or "jelly fungi", since many have gelatinous basidiocarps that produce spores on septate basidia. Around 200 species are known worldwide, placed in six or more families, though the status of these families is currently uncertain. All species in the Auriculariales are believed to be saprotrophic, most growing on dead wood. Fruit bodies of several Auricularia species are cultivated for food on a commercial scale, especially in China.

The Auriculariaceae are a family of fungi in the order Auriculariales. Species within the family were formerly referred to the "heterobasidiomycetes" or "jelly fungi", since many have gelatinous basidiocarps that produce spores on septate basidia. Around 100 species are known worldwide. All are believed to be saprotrophic, most growing on dead wood. Fruit bodies of several Auricularia species are cultivated for food on a commercial scale, especially in China.

The Tremellales are an order of fungi in the class Tremellomycetes. The order contains both teleomorphic and anamorphic species, most of the latter being yeasts. All teleomorphic species in the Tremellales are parasites of other fungi, though the yeast states are widespread and not restricted to hosts. Basidiocarps, when produced, are gelatinous.

Pucciniomycetes is a diverse class of fungi in the subphylum Pucciniomycotina of phylum Basidiomycota. The class contains 5 orders, 21 families, 190 genera, and approximately 8,016 species. It has been estimated that this class contains about one third of all teleomorphic basidiomycetes. Pucciniomycetes contains many economically important plant pathogenic fungal rusts; the order Pucciniales is the largest clade in this class, representing approximately 7,000 species.

Ceratobasidium is a genus of fungi in the order Cantharellales. Basidiocarps are effused and the genus is sometimes grouped among the corticioid fungi, though species also retain features of the heterobasidiomycetes. Anamorphic forms were formerly referred to the genus Ceratorhiza, but this is now considered a synonym of Rhizoctonia. Ceratobasidium species, excluding the type, are also now considered synonymous with Rhizoctonia and some species have been transferred to the latter genus. Species are saprotrophic, but several are also facultative plant pathogens, causing a number of commercially important crop diseases. Some are also endomycorrhizal associates of orchids.

Rhizoctonia is a genus of fungi in the order Cantharellales. Species form thin, effused, corticioid basidiocarps, but are most frequently found in their sterile, anamorphic state. Rhizoctonia species are saprotrophic, but some are also facultative plant pathogens, causing commercially important crop diseases. Some are also endomycorrhizal associates of orchids. The genus name was formerly used to accommodate many superficially similar, but unrelated fungi.

<span class="mw-page-title-main">Tulasnellaceae</span> Family of fungi

The Tulasnellaceae are a family of fungi in the order Cantharellales. The family comprises mainly effused (patch-forming) fungi formerly referred to the "jelly fungi" or heterobasidiomycetes. Species are wood- or litter-rotting saprotrophs, but many are also endomycorrhizal associates of orchids and some have also been thought to form ectomycorrhizal associations with trees and other plants.

Sistotrema is a genus of fungi in the family Hydnaceae. The genus contains at least 55 species and has a worldwide distribution. The type species is Sistotrema confluens Pers. (1794).

Amylocorticiales is an order of fungi in the class Agaricomycetes. The order was circumscribed in 2010 to contain mostly resupinate (crust-like) forms that have been referred to genera Anomoporia, Amyloathelia, Amylocorticiellum, Amylocorticium, Amyloxenasma, Anomoloma, Athelopsis, Ceraceomyces, Hypochniciellum, Leptosporomyces and Serpulomyces and the anomalous species, Athelia rolfsii, now classified in its own genus, Agroathelia.

The Pachnocybe are a genus of fungi, within the monotypic family of PachnocybaceaeOberw. & R.Bauer, 1989, and within the monotypic order of Pachnocybales, within the class Pucciniomycetes. They are parasitic on plants or saprobic on rotten wood.

Platygloea is a genus of fungi belonging to the class Pucciniomycetes. Basidiocarps of the type species are disc-shaped, gelatinous, and occur on dead wood, probably as a saprotroph. Microscopically, all species of Platygloea sensu lato have auricularioid basidia. Currently the genus contains a heterogeneous mix of auricularioid fungi not yet accommodated in other genera.

Sirobasidium is a genus of fungi in the order Tremellales. Basidiocarps are gelatinous and appear to be parasitic on ascomycetous fungi on wood. Microscopically they are distinguished by producing septate basidia in chains which give rise to deciduous sterigmata. Species are distributed worldwide.

References

1 2 3 4 5 6 7 8 Swann EC; Taylor JW (1993). "Higher Taxa of Basidiomycetes: An 18S rRNA Gene Perspective". Mycologia. 85 (6): 923–936. doi:10.2307/3760675. JSTOR 3760675.
1 2 3 Hibbett DS; et al. (2007). "A higher-level phylogenetic classification of the Fungi". Mycological Research. 111 (5): 509–547. CiteSeerX 10.1.1.626.9582 . doi:10.1016/j.mycres.2007.03.004. PMID 17572334. S2CID 4686378.
1 2 Lowy B (1968). "Taxonomic Problems in the Heterobasidiomycetes". Taxon. 17 (2): 118–127. doi:10.2307/1216500. JSTOR 1216500.
1 2 Patouillard NT (1900). Essai taxonomique sur le families et les generes des Hymenomycetes. Paris, France: Lons-le-Saunier.
1 2 3 Wells K (1994). "Jelly Fungi, Then and Now!". Mycologia. 86 (1): 18–48. doi:10.2307/3760717. JSTOR 3760717.
↑ Talbot PHB (1968). "Fossilized pre-Patouillardian taxonomy". Taxon. 17 (6): 620–628. doi:10.2307/1218002. JSTOR 1218002.
↑ Donk MA (1972). "The heterobasidiomycetes: a reconnaissance. I. A restricted emendation". Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen Series C. 75 (5): 365–375. PMID 4264769.
↑ Donk MA (1972). "The Heterobasidiomycetes: a reconnaissance. II. Some problems connected with the restricted emendation". Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen Series C. 75 (5): 376–390. PMID 4264770.

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[Swann_&_Taylor_1993-1] 1 2 3 4 5 6 7 8 Swann EC; Taylor JW (1993). "Higher Taxa of Basidiomycetes: An 18S rRNA Gene Perspective". Mycologia. 85 (6): 923–936. doi:10.2307/3760675. JSTOR 3760675.

[Hibbett_et_al_2007-2] 1 2 3 Hibbett DS; et al. (2007). "A higher-level phylogenetic classification of the Fungi". Mycological Research. 111 (5): 509–547. CiteSeerX 10.1.1.626.9582 . doi:10.1016/j.mycres.2007.03.004. PMID 17572334. S2CID 4686378.

[Lowy_1968-3] 1 2 Lowy B (1968). "Taxonomic Problems in the Heterobasidiomycetes". Taxon. 17 (2): 118–127. doi:10.2307/1216500. JSTOR 1216500.

[Patouillard_1900-4] 1 2 Patouillard NT (1900). Essai taxonomique sur le families et les generes des Hymenomycetes. Paris, France: Lons-le-Saunier.

[Wells_1994-5] 1 2 3 Wells K (1994). "Jelly Fungi, Then and Now!". Mycologia. 86 (1): 18–48. doi:10.2307/3760717. JSTOR 3760717.

[Talbot_1968-6] Talbot PHB (1968). "Fossilized pre-Patouillardian taxonomy". Taxon. 17 (6): 620–628. doi:10.2307/1218002. JSTOR 1218002.

[Donk_1972a-7] Donk MA (1972). "The heterobasidiomycetes: a reconnaissance. I. A restricted emendation". Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen Series C. 75 (5): 365–375. PMID 4264769.

[Donk_1972b-8] Donk MA (1972). "The Heterobasidiomycetes: a reconnaissance. II. Some problems connected with the restricted emendation". Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen Series C. 75 (5): 376–390. PMID 4264770.

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