Classification of Higher Fungi

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

The somatic phase consists mostly of a mycelium which is usually septate. The septa have each a central pore and thus are incomplete. No motile cells are produced in the life cycle.

The higher fungi comprise the following three classes:

1. Class Ascomycetes:

The characteristic spores of the sexual or perfect stage are endogenous in origin and are called the ascospores. They are produced within special, sac-like structures called the asci. Plasmogamy takes place by the fusion of gametangia or somatic hyphae. Somatic phase is usually a septate mycelium which multiplies asexually by conidia; rarely it is unicellular (as in the yeasts) and is propagated by budding or rarely by fission.

2. Class Basidiomycetes:

The characteristic spores of the sexual or perfect stage are exogenous in origin and are called the basidiospores. They are borne externally usually on club-shaped structures called basidia. The somatic phase consists of a simple or complex mycelium with or without clamp connections. Sexual organs are lacking. Plasmogamy, however, takes place by hyphal fusion.

3. Form-class Deuteromycetes or Fungi Imperfecti:

Included in this class are the higher fungi in which the sexual or perfect stage is unknown. The somatic phase consists of a septate mycelium which multiplies asexually by conidia. The conidia are produced on conidiophores which may occur isolated or may be aggregated to form complex structures such as synnema, pycnidia and acervuli.

The classification of Fungi outlined above has been followed in this text. However, for the benefit of the students a brief account of the classification proposed by Alexopoulos and Mims (1979) is given here.

They place the fungi including the slime molds in the Kingdom Mycetae of the super kingdom Eukaryota which, in addition, includes four other kingdoms.

They divide the Kingdom Mycetae into three divisions namely:

(i) Gymnomycota

(ii) Mastigomycota, and

(iii) Amastigomycota.

The division is subdivided into subdivisions, classes, sub-classes and orders.

Division I. Gymnomycota:

It includes phagotrophic organisms devoid of cell walls. This division comprises two subdivisions. These are Acrasiogymnomycotina and Plasmodiogymnomycotina.

Subdivision 1:

Acrasiogymnomycotina. It includes a single class Acrasiomycetes.

Class 1:

Acrasiomycetes. Lacks flagellated cells except one species. The class comprises two sub-classes Acrasiomycetidae and Dictyosteliomycetidae.

Subdivision 2:

Plasmodiogymnomycotina.

It is split into two classes:

Class 1:

Protosteliomycetes.

Class 2:

Myxomycetes:

It includes the true slime mold and comprises three sub­classes namely.

Sub-class 1:

Ceratiomyxomycetidae:

It includes one order Ceratiomyxales.

Sub-class 2:

Myxogasteomycetidae:

It comprises four orders namely, Liceales, Echinosteleales, Trichlales & Physarales.

Sub-class 3:

Stemonitomycetidae with one order Stemonitales.

Division II:

Mastigomycota:

Includes fungi with absorptive nutrition, unicellular or filamentous, mycelium coenocytic.

It comprises two subdivisions:

Class 1:

Haplomastigomycotina:

Includes fungi with uni-orbi-flagellate zoospores.

It comprises 3 classes:

Class 1:

Chytridiomycetes:

Fungi producing zoospores furnished with a single whiplash flagellum inserted at the posterior end.

Class 2:

Hyphochytridiomycetes:

Motile cells with a single tinsel flagellum inserted at the anterior end.

Class 3:

Plasmodiophoromycetes:

Parasitic fungi producing biflagellate motile cells with both the flagella of whiplash type inserted at the anterior end.

Subdivision 2:

Diplomastigomycotina:

Sexual reproduction oogamous, zoospores biflagellate, meiosis gametangial.

This subdivision includes a single class:

Class 1:

Oomycetes:

It comprises four orders namely, Lagenidiales, Saprolegniales, Leptomitales and Peronosporales.

Division III:

Amastigomycota:

Fungi with absorptive nutrition, motile cells lacking, mycelium aseptate or septate. This division includes four subdivisions, namely Zygomycotina, Ascomycotina, Basidiomycotina and Deuteromycotina.

Subdivision 1:

Zygomycotina with two classes:

Class 1:

Zygomycetes:

It includes six Orders.

Class 2:

Trichomycetes:

It comprises five orders.

Subdivision 2:

Ascomycotina:

Fungi usually with a septate mycelium producing haploid ascospores in sac-like cells called Asci.

This subdivision is represented by a single class:

Class Ascomycetes:

It is subdivided into five subclasses as follows:

Subclass 1:

Hemiascomycetidae comprising three orders.

Subclass 2:

Plectomycetidae with five orders.

Subclass 3:

Hymenoascomycetidae with ten orders.

Subclass 4:

Laboulbeniomycetidae including two orders

Subclass 5:

Loculoascomycetidae with five orders.

Subdivision 3:

Basidiomycotina:

Septate mycelium produces basidiopores (meiospores) exogenously on various types of basidia.

The subdivision includes a single class.

Class 1:

Basidiomycetes:

It is split into three subclasses:

Subclass 1:

Holobasidiomycetidae:

Phragmobasidiomycetidae

Subclass 3:

Teliomycetidae.

Subdivission 4:

Deuteromycotina:

It includes imperfect fungi in which sexual stage is unknown.

It comprises a single form class.

Form class 1:

Deuteromycetes with three form subclasses namely Blastomycetidae, Coelomycetidae, and Hyphomycetidae.

Lichens:

Ascomycetous, Basidiomycetous and Deuteromycetous mycobionts, symbiotically associated with green or blue-green algae (phycobionts), form various types of thalli.

A more natural system of classification of fungi was proposed by Ainsworth (1973) which has been accepted by many mycologists of today like Webster (1980), Bilgrami (1985) and Dube (1987). Ainsworth placed all the fungi in the kingdom Mycota.

His classification is as follows: