In this article we will discuss about the classification of division mycota.
The mycologists place division Mycota in the kingdom Plantae.
This division includes non-green (achlorophyllous) nucleated thallophytes (fungi) which are characterised by the following features:
(a) Obtain nutrition either by living as saprophytes or as parasites. Lacking chlorophyll, the mode of nutrition is thus heterotrophic and absorptive except slime molds in which it is phagotrophic.
(b) Somatic phase may be filamentous, unicellular or a Plasmodium.
(c) Presence of a true nucleus with a nuclear membrane and nucleoli in the cell.
(d) Typically the cell wall is chitinised but some Oomycetes have a cellulose cell wall.
(e) Reserve food accumulates in the form of glycogen and not starch. In addition there are oil drops.
(f) Reproduce both by asexual and sexual methods.
The division Mycota includes two sub-divisions, Myxomycotina and Eumycotina.
I. Subdivision Myxomycotina:
This subdivision includes the slime molds which possess the following distinctive features:
(i) The thallus is a non-green, multinucleate mass of protoplasm called the Plasmodium.
(ii) The Plasmodium lacks a definite cell wall, and thus is amoeboid in shape.
(iii) It is free living, diploid and holocarpic.
(iv) The propagative units (spores) are differentiated by meiosis.
All the free-living slime molds are placed in the class Myxomycetes.
II. Subdivision Eumycotina:
All the other fungi except the slime molds are included in this subdivision. It is a heterogeneous group comprising about 80,000 known species.
They are distinguished as below:
(i) With the exception of a few unicellular forms, the somatic phase is typically a filamentous structure called the mycelium.
(ii) The unit of structure of the thallus or mycelium is not a cell but a hypha.
(iii) The cell or hyphal wall is usually composed of fungus cellulose (chitin) or a mixture of cellulose and chitin or rarely of cellulose.
(iv) There is a definite nucleus with a nuclear membrane and nucleoli in the cell.
(v) Excepting a few, all are eucarpic.
(vi) The septa between the cells when present have each a central pore.
(vii) The growth in length in the filamentous forms is apical.
(viii) Reproduce both by asexual and sexual methods.
(ix) Asexual reproduction or sporulation takes place by mitospores which may be motile or non-motile.
(x) There is gradual and progressive simplification and ultimate elimination of the sexual apparatus from the lower to the higher forms.
The older mycologists divide the subdivision Eumycotina, which includes the true fungi, into four classes, namely, Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes. This scheme of classification of true fungi is still in vogue in many countries.
The modern mycologists, however, consider that the class Phycomycetes, which includes all the lower fungi, is not a natural group of closely related forms. Alexopoulos (1962), therefore, took a logical step and split the lower fungi included in the class Phycomycetes into six classes.
An outline scheme of classification of Eumycotina (ture fungi) followed in this edition of the text, is set out below. It is customary to divide the true fungi into two main groups, the lower and the higher Fungi.