Classification of Fungi

The classification of the fungi is a very challenging task since it presents various problems that originate from the differences of opinion of different workers.

The situation becomes even more difficult as we learn new facts about the fungi, which often demand a change in the concept of their relationship and reclassification.

As the classification includes the grouping of different fungi and naming them according to the internationally accepted system, there are so many classifications of fungi. Such as-

  • Gwynne-Vaughan and Barnes system (1926)
  • E. A. Bessey system (1950)
  • G. M. Smith system (1955)
  • Alexopoulos system (1962)

Fungi are divided by most of the authors into four main classes. However, the classification of fungi introduced by Gwynne-Vaughan and Barnes is the most standard and widely accepted.

Classification of Fungi

Gwynne-Vaughan and Barnes System of Classification of Fungi

Gwynne-Vaughan and Barnes divided fungi into four classes on the basis of the septation of mycelium and the characteristics of spores.

The outline of the classification is given below:

  • Class 1. Phycomycetes
  • Subclass 1. Archimycetes
    • Order 1. Chytridiales
    • Order 2. Acrasiales
    • Order 3. Protomycetales
  • Subclass 2. Oomycetes
    • Order 1. Blastocladiales
    • Order 2. Monoblepharidales
    • Order 3. Leptomitales
    • Order 4. Saprolegniales
    • Order 5. Peronosporales
  • Subclass 3. Zygomycetes
  • Class 2. Ascomycetes
  • Series 1. Plectomycetes
    • Order 1. Plectascules
    • Order 2. Erysiphales
    • Order 3. Exoascules
  • Series 2. Discomycetes
    • Order 1. Pezizales
    • Order 2. Helevellales
    • Order 3. Tuberales
    • Order 4. Phacidiales
    • Order 5. Hysteriales
  • Series 3. Pyrenomycetes
    • Order 1. Hypocreales
    • Order 2. Dothideales
    • Order 3. Laboulbeniales
    • Order 4. Sphaeriales
  • Class 3. Basidiomycetes
  • Subclass 1. Hemibasidiomycetes
    • Order 1. Ustilaginales
  • Subclass 2. Protobasidiomycetes
    • Order 1. Uredinales
    • Order 2. Tremellales
    • Order 3. Agaricales
  • Subclass 3. Autobasidiomycetes
    • Order 1. Hymenomycetales
    • Order 2. Gasteromycetales
  • Class 4. Deuteromycetes
    • Order 1. Hyphomyceles
    • Order 2. Melanconiales
    • Order 3. Sphaeropsidales
Classification of fungi in word diagram
Figure: Classification of fungi, adopted from Gwynne-Vaughan and Barnes, 1926

Class 1. Phycomycetes (Lower Fungi)

  • The vegetative thallus is simple. It is either unicellular or filamentous.
  • The mycelium may be absent, rudimentary, or well developed.
  • Reproduces asexually usually by motile cells.
  • Sexual spores are zygospores and oospores.

Subclass 1. Archimycetes

  • Mycelium is either absent or rudimentary.
  • The hyphal wall contains chitin and glucan.
  • Motile cells have a single whiplash type of flagellum inserted at the posterior end.
  • Example: Synchytrium, Olpidium.

Subclass 2. Oomycetes (Oogamous Fungi)

  • The mycelium is well developed, multinucleate, and aseptate, i.e., coenocytic in nature.
  • The cell wall possesses cellulose and glucan. Chitin, or fungus cellulose, is also found in some members.
  • Asexual spores (zoospores) develop within spore sacs or sporangia.
  • The spores are often motile.
  • Motile cells are biflagellate. One flagellum is of tinsel type which points forward, and the other is of whiplash type.
  • Sexual reproduction takes place by gametangial contact, which results in the formation of oospore.
  • Examples: Pythium, Saprolegnia, Phytophthora.

Subclass 3. Zygomycetes (Conjunction Fungi)

  • The mycelium is multinucleate and aseptate.
  • The hyphal wall consists of chitin and chitosan.
  • Accessory spores are non-motile.
  • Asexual reproduction occurs through sporangiospores. These spores are formed inside the sporangia borne at the tips of special hyphae called sporangiophores.
  • The gametes are multinucleate and are known as coenogametes.
  • Sexual reproduction takes place by gametangial copulation or conjugation results in the formation of zygospore.
  • Examples: Rhizopus, Pilobolus, Mucor.

Class 2. Ascomycetes (Sac Fungi)

  • The mycelium is well developed and consists of septate hyphae (Except Yeast, it is unicellular). Septa is simple type.
  • Hyphal wall possesses chitin or fungus cellulose.
  • Principal spores or sexual spores are known as ascospores. They are produced endogenously within a special sac-like structure called the ascus.
  • Sexual reproduction takes place by fusion of gametangial or somatic hyphe.
  • Asexual reproduction usually occurs by conidia. In unicellular Yeast, it takes place through budding or fission.
  • Nutritionally, the members of ascomycetes are saprotrophic, coprophilous, or parasitic.

Series 1. Plectomycetes

  • Ascocarp is of the cleistothecium type. It is closed and spherical.
  • Asci are irregularly arranged inside the ascocarp.
  • Examples: Penicillium, Saccharomyces, Erysiphe, Taphrina, Aspergillus.

Series 2. Discomycetes

  • Ascocarp is of the apothecium type. It is cup-shaped or saucer-shaped and wide open when ripe.
  • Asci in ascocarp lie side by side, parallel to each other.
  • Examples: Peziza, Ascobolus, Helvella, Genea, Lophodermium.

Series 3. Pyrenomycetes

  • Ascocarp is of the perithecium type. It is flask-shaped and open at the apex by a pore called an ostiole.
  • Asci are arranged parallelly.
  • Examples: Claviceps, Nectria, Phyllachora, Xylaria, Laboulbenia, Coreomyces.

Class 3. Basidiomycetes (Club Fungi)

  • Most advanced group of fungi.
  • Mycelium is well developed, branched, and septate.
  • Septa may be simple or dolipore.
  • Usually, two types of mycelia are seen in this group. One is primary, and the other is secondary mycelium.
  • In the primary mycelium, the cells are monokaryotic, i.e., cells contain a single haploid nucleus. While secondary mycelium contains dikaryotic cells, i.e., cells with two nuclei.
  • The cell wall mainly contains chitin and glucans.
  • Motile cells are absent.
  • The principal spores are basidiospores. They originate exogenously and are borne externally on club-shaped structures called basidia.
  • Sex organs are absent.
  • Plasmogamy takes place by hyphal fusion.
  • Most members are saprophytes or parasites.

Subclass 1. Hemibasidiomycetes

  • The number of basidiospores is indefinite.
  • Examples: Ustilago, Tilletia.

Subclass 2. Protobasidiomycetes

  • Basidium is septate.
  • The number of basidiospores produced by basidium is definite.
  • Examples: Puccinia, Tremella, Auricularia.

Subclass 3. Autobasidiomycetes

  • The number of basidiospores is 4 (definite).
  • Basidium is aseptate.
  • Examples: Agaricus, Polyporus, Phallus, Lycoperdon.

Class 4. Deuteromycetes (Imperfect Fungi)

  • It is a synthetic group of fungi.
  • The fungi are mostly multicellular.
  • The mycelium is septate.
  • Asexual reproduction takes place mainly by conidia.
  • Sexual reproduction or perfect stage is completely absent or not known. Therefore, the class deuteromycetes is called Fungi imperfecti.
  • The members of this class are saprophytes or parasites.
  • Examples: Fusarium, Alternaria, Helminthosporium.

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