In this article we will discuss about the classification of Fungi Imperfecti.
The classification of Fungi Imperfecti is completely artificial. It separates many genera, which had their sexual stages been known, would have been near each other. It is based on their conidial peculiarities and bears no connection to their sexual stage not to their origin or evolution. It cannot, therefore, be called a natural classification. Such a system shows no relationship.
It is better to call it a key which helps in cataloguing or identifying them. Deuteromycetes thus is an artificial class created for convenience to include fungi which do not fit in the other groups of fungi.
This system of classification is therefore known as Artificial system of classification and is mainly based on conidial characters. The naming of the conidial stages is so perfectly convenient that International Botanical Congress at its 1950 meeting held at Stockholm decided to legalise it, still recognising of course the name of the perfect stage for the entire organism as and when discovered.
In accordance with conidial characters, P.A. Saccardo (1880-1886) proposed a system of classification which has been used ever since it was proposed and is still popular.
He divided the class into four orders viz. Moniliales (Conidia produced directly on hyphae or on conidiophores), Meianconiales (conidia produced in acervuli), Sphaeropsidales (conidia produced in pycnidia) and Mycelia Sterilia (conidia lacking).
Moniliales were further divided into four families, Melanconiales into one and Sphaeropsidales into four families. Each family was also divided into sections based on septation and shape of conidia.
These sections are: Amerosporae (conidia one celled), Allantosporae (conidia cylindric, curved), Hyalosporae (conidia hyaline), Phaeosporae (conidia coloured), Didymosporae (conidia ovoid to oblong, one septate, hyaline or coloured), Phragmosporae (conidia with 2 or more cross septa), Dictyosporae (conidia muriform, hyaline or coloured), Scolecosporae (conidia filiform), Staurosporae (conidia star shaped) and Helicosporae (conidia helical).
Subsequent mycologists used the word “form” as a prefix before the subdivisions, class, order, family, genus and species to denote the artificial and temporary nature of this class of Fungi.
The characters on which classification of the Form-class Fungi Imperfecti is based are:
(i) Presence or absence of conidia,
(ii) Colour, shape and septation of conidia, and
(iii) Kind of asexual fruiting body.
On the basis of these characters the form-class Deuteromycetes is divided into the following four form orders:
1. Form-order Moniliales (or Hyphomycetes):
Conidia are usually borne freely on the mycelium or on free conidiophores arising from the mycelium. In some cases conidiophores are grouped into sporodochia or synnemata.
Reproduction by budding and oidia formation also takes place. This form-order includes both saprophytes and parasites.
2. Form-order Sphaeropsidales (or Photomitales):
Conidia are produced within small, globose or flask-shaped pycnidia or modifications of such structures. It includes plant parasites.
3. Form-order Melanconiales:
Conidia are produced singly or in chains from conidiophores packed closely to form an asexual fructification called an acervulus. It includes plant parasites.
4. Form-order Mycelia sterilia:
This form-order included 20 genera and 200 form species. They are imperfect fungi in which special reproductive stages including the conidia are totally absent. They reproduce by sclerotia, rhizomorphs and other vegetative means.
Ainsworth (1973) proposed a system of classification which is now accepted by most mycologists.
According to this classification, the Subdivision Deuteromycotina has been divided into three classes as follows:
