Modern Classification of Fungi, Biology tutorial


There is a vital look of the prior basis of categorization vis-a-vis modern categorization that takes into consideration evolutionary relationship. Fungi were widely categorized into two classes:

1) Lower fungi 

2) Higher fungi

Fungi are categorized on morphology and physiology into Acrasiomycetes (or Cellular slime moulds), Myxomycetes (or True slime moulds), Phycomycetes (or Lower fungi), which comprises of Chytriomycetes, Oonmycetes, Zygomycetes and Eumycetes (that is, the Higher fungi) comprising of Ascomycetes and Basidiomycetes. There are eight classes in the sub-division Eumycotina that differ from class A to I.

The modern categorization comprises of five main divisions that are Mastigocotina, Ascomycotina, Amastigomycotina, Basidiomycotina and Deuteromycotina. Nigerian categorization employs various parameters that are descriptive, texture, shape habitat, season, flavor and also legendary status.

Amplification of the Classification of Fungi:

In the primitive categorization, the first class is the lower fungi that encompass their vegetative mycelia that are coenocytic or aseptate. A few are unicellular and vegetative mycelium ranges from the simple rhizoid to somatic cell and to even very intricate anaesomes of rhizomycellium.

The higher group of lower fungi though has well-developed hyphal system, generally coenocytic and are just endowed having septa to cut off the reproductive structure. The second class is the higher fungi having the vegetative mycelium generally septate. In this class, the mycelium becomes distinguished into fruiting bodies that are generally visible and conspicuous. Edible mushroom are extensions of the mycelium. Two main groups are known and distinguished in the higher fungi. 

1) The Ascomycetes in which the features spore in the perfect phases are endogenous. Such spores are bound in sacs termed as asci. The imperfect phases produce conidia that are extensions of aerial mycelium.

2) The Basidiomycetes in which the features spore in the perfect phase is exogenous and is found in fruiting bodies termed as basidiocarp. The fruiting body of most basidiomycetes builds up from a subterranean mycelium and grows outward to distinguish in pileus that houses the gills or lamella from where basidia develop.

Though, some higher fungi can be unicellular example: Yeast. In times of regular nomenclature, the lower fungi fall into the class Phycomcetes, whereas the higher fungi are composed of the Ascomycetes and Basidiamycetes.

Such terms where conveniently used fungi past but of recent new terms are employed. Fungi are now placed in a division termed as mycota. There are some subdivisions, one of which is Myxomycotina that is a sub-division which comprises the slime moulds. The vegetative structure termed as plasmodium is a multinucleate mass of cytoplasm unbounded through rigid walls that flow in amoeboid fashion over the surface of the substrate, ingesting smaller microorganism and fragments of decaying plant material. A few slime moulds are plasmodial in the shape and form aerial hyphae.

The sub-division Eumycotina comprises of the true fungi that are mostly filamentous. There are eight (8) classes which are recognized that are numbered A to I class.

Class A: Chytridiomycetes. This class comprises fungi which encompass a single posterior whip-like flagellum.

Class B: Oomycetes: Fungi in this class encompass zoospores which encompass two flagella. The anterior flagellum is whip-lash like whereas the other is tinsel shaped.

Class C:  Plasmodiophoromycetes: In this class the motile cells encompass two anterior whiplash-like flagella.

Class D: The Zygomycetess: Fungi in this class encompass coencytic hyphae, septate at the point of reproduction and the sexual reproductive form that it derives its name from by the fusion of two gametangia.

Class E: Trichomyces: Fungi in this class are filamentous that are found in the guts or cuticle of the arthropods.

Class F: Ascomycetes: Fungi in this class encompass septate hyphae. The imperfect phases develop conidia and the perfect phase generates ascospores.  The nature of fruiting body can be very varied however the characteristic feature is the growth of ascospores. The mycelium differs however in certain cases no mycelium is generated example: in yeast. In a number of them, there are fruiting bodies that are saucer - shaped and are usually termed as apothecium, where the ascocarp or fruiting body takes place as a flat surface or hollow saucer. The ascocarp distinguishes into an upper portion having the asci and the lower portion made up of pseudoparenchyma cell.  

In some others, the fruiting body is similar to a wine glass that holds the fruiting body in position and serves up for conduction of nutrients.

In the third group, the fruiting body has been distinguished into a sporogenous body, the stalk and the subterranean hyphae.

In the fourth group, the fruiting body is similar to a flask that encloses the asci.

This flask - shape ascocarp might or might not encompass an ostiole (hole). It might have a neck which ends in an opening and the nature of the fruiting body can be employed in categorizing fungi in this class. 

Class G: Basidiomycetes: The characteristic trait of this is the possession of basidia. The fruiting body is highly specialized. In this group is the edible mushroom, the bracket fungi, the puffballs, the parasitic rusts and smuts that are devastating to trees and grasses.

Class H: Deuteromycetes: This is a combination of the class ascomycetes and basidiomycetes that sexual or perfect phases have not yet been discovered. The imperfect phase is characterized and given the similar kind of name as ascomycetes. Though, when the perfect phase is discovered, they either fall into ascomycetes or basidiomycetes and the suitable name is then given. When the perfect phase is discovered the name assigned to the perfect phase becomes the recognized name.

Class I: Lichens: In this class, a situation occurs in which there is a symbiotic relationship between algae or Cyanobacteria by ascomycetes or basidiomycetes. Lichens are composite organisms comprised of algae and fungi, each contributing to the advantages of the other or both. The algae synthesize vitamins and carbohydrates by photosynthesis and get other nutrients (that is, water and minerals and moist sheller) from the fungi whereas the fungi based on the algae for organic carbon.

Modern Classification:

In the modern classification fungi are categorized into six main divisions which comprise the:

1) Mastigomycotina which comprises of chytridiomycetes and Oomycetes 

2) Amstigomycotina which consists of Zygotes. The two classes above were regarded as phymycetes that is, the lower fungi.

3) Ascomycotina comprises of Hemi-ascomycetidae Plenomycetidae and other classes such as Pyrenomycetes and Discomycetes.

4) Basidiomycotina which consists of two orders which are the (i) Aphylophrales (Bracket fungi) and (ii) Agaricales. The two divisions Ascomycotina and Basidiomycotina are regarded as higher fungi.

5) Deuteromycotina formerly termed as Deuteromycetes are termed as fungi imperfect.

6) The Lichens.

Higher fungi:

Subdivision 3: Ascomycotina

Class 1: Hemiascomycetes

Order 1: Ascomycetales

Order 2: Taphrinales

Class 2: Pyrenomycetes

Order 1: Erysiphales - example: Erysiphe gramminis

Order 2: Shaeriales

Order 3: Hypocreales

Class 3: Loculoascomycetes

Order 1: Myriangiales

Order 2: Dothiodiales

Order 3: Pleosporales

Subdivision 4: Basidiomycotina

Class 1: Hemibasidiomycetes

Order 1: Ustilaginales example: Ustilago spp.

Order 2: Uredinales

Class 2: Hymenomycetes

Order 1: Exobasidales 

Order 2: Agaricales e.g. Agaricus spp, Pleurotus spp.

Order 3: Tulasnellales

Order 4: Aphyllophorales

Subdivision 5: Deuteromycotina (fungi imperfecti)

Class 1: Coelomycetes

Order 1: Melanconiales

Class 2: Hyphomycetes

Order 1: Hyphales example: Alternaria cercospora spp.

Class 3: Agonomycetes

Order: Agonomycetales example: Rhizoctoma spp.

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