Classification of Fungi| Botany

In this article we will discuss about the classification of fungi.

The classification of fungi is still in a state of flux. A stable and ideal system of classification is yet to be proposed. Many systems have been proposed from time to time by mycologists. With the advancement of knowledge newer systems are proposed while the older ones are discarded.

The classification of fungi is mostly based on the features noted below:

(a) Nature of somatic phase whether unicellular or a mycelium, if latter septate or aseptate.

(b) Kinds of asexual spores (mitospores)-sporangiospores or conidia; if former motile or non-motile; number, form and arrangement of flagella in the motile spores.

(c) Kinds of sporangia.

(d) Nature of the life cycle-whether asexual, haplontic, diplontic, haplodiplonitc or haploid dikaryotic.

(e) Presence or absence of the perfect or sexual stage.

It was probably Bauhin who for the first time tried to classify fungi in his book Pinax Theatri Botanici (1623) wherein he described 100 species of fungi. Later, fungi were divided into six classes by Tournefort (1694) in his book Elements de Botanique while Carolus Linnaeus (1753) placed all fungi in his 24^th class Cryptogamia in his famous book Species plantarum.

The first detailed classification of fungi, however, was proposed by Elias Magnus Fries in his three volume book Systema Mycologicum published during 1821-1832.

He divided fungi into four classes:

(i) Coniomycetes

(ii) Hyphomycetes

(iii) Gastromycetes and

(iv) Hymenomycetes.

Saccardo (1882) included Bacteria and slime molds in fungi in his famous book Sylloge Fungorum and divided fungi into six classes:

(i) Schizomycetes

(ii) Myxomycetes

(iii) Phycomycetes

(iv) Ascomycetes

(v) Basidiomycetes and

(vi) Deuteromycetes.

Gwynne-Vaughan and Barnes (1926) rejected the contention of Saccardo and excluded bacteria and slime molds from fungi. Slime molds were treated as Forms resembling Fungi. They recognised only four classes of fungi on the basis of structure of mycelium and characteristics of spores.

These four classes are:

(i) Phycomycetes:

Mycelium aseptate and multinucleate, sexual spores are Oospores and Zygospores.

(ii) Ascomycetes:

Mycelium fairly branched and septate; Septa simple; Characteristic Spores are endogenously produced ascospores.

(iii) Basidiomycetes:

Mycelium branched and septate with Dolipores, Characteristic spores are exogenously produced basidiospores.

(iv) Deuteromycetes:

Mycelium branched and septate, sexual spores absent.

Gaumann and Dodge (1928), who also did not include slime molds in Fungi, proposed a system of classification based on the life-cycle and development of fructification. According to them.

Fungi were divided into the following four classes:

(i) Archimycetes:

Thallus naked.

(ii) Phycomycetes:

Thallus with definite cell wall.

In both the above classes zygote is the diploid stage and meiosis occurs at its germination.

(iii) Ascomycetes:

Thallus more highly developed plasmogamy results in a distinct mycelium; Karyogamy delayed; meiosis takes place in a distinct structure leading to the formation of sporangial structures called asci producing endogenously the ascospores.

(iv) Basidiomycetes:

Thallus more highly developed consisting of dikaryotic mycelium in the somatic phase; meiosis shifted to a much later stage in a structure called conidiophores or basidia exogenously producing basidiospores.

Bessey (1950) agreed with De Bary (1887) and placed the slime molds under the name Mycetozoa. His system of classification was largely based on the reproductive characters.

True fungi were divided as follows:

1. Lower Fungi:

Fruit bodies not formed. Only one class Phycomyceteae.

2. Higher Fungi.

Fruit bodies are formed, divided into three classes:

(i) Ascomyceteae Fruit body asci; ascospores endogenously formed.

(ii) Basidiomyceteae Fruit body basidia; basidiospores formed exogenously.

(iii) Deuteromycetae. Sexual stage absent.

The practice of dividing Fungi into four classes continued till 1958 when Sparrow (1958) created nine classes emphasising the importance of flagellation of the zoospores in the classification. He considered that flagellation should be treated as a good taxonomic and phylogenetic criterion.

These nine classes are:

(i) Chytridiomycetes

(ii) Hyphochytridiomycetes

(iii) Plasmodiophoromycetes

(iv) Oomycetes

(v) Zygomycetes

(vi) Trichomycetes

(vii) Ascomycetes

(viii) Basidiomycetes, and 

(ix) Deuteromycetes.

Again in 1961 Martin proposed a system of classification based on the septation of mycelium and spore characters.

The classification proposed by him is as follows:

It would be clear from the above that modem mycologists are unanimous on the exclusion of bacteria from the fungi on the basis of lack of a true nucleus in the bacterial cell. There is a difference of opinion as regards the slime molds. Many mycologists favour their inclusion among the fungi.

The Committee on the International Rules of Botanical Nomenclature has made the following recommendations:

(a) The names of divisions of fungi should end in-mycota.

(b) The sub-divisions should end in-mycotina.

(c) The names of classes should have a suffix-mycetes.

(d) The sub-classes should end with a suffix-mycetideae.

(e) The names of orders should end in-ales.

(f) The families should end with a suffixaceae.