Classification of Fungi

On the basis of the organisation of the vegetative thallus, the morphology of reproductive structures, the way of spores production and particular life cycle involved the kingdom mycota is classified into following divisions.

Phycomycetes

It includes the simplest type of fungi. It is also called as Algae-Fungi because most of the characteristics of them are similar to algae like Vaucheria.

General characteristics:

• They have simple thallus which is unicellular or coenocytic or aseptate filaments.
• They reproduce asexually by the formation of zoospores or non-motile spores.
• Sexual reproduction is isogamous or heterogamous which takes place by gametangial contact.
• The diploid phase is represented by zygote.

Phycomycetes has been classified into subclasses: oomycetes and zygomycetes.

Oomycetes

General Characteristics

• Oomycetes range from a primitive unicellular thallus to a profusely branched filamentous mycelium.
• Many members of them are terrestrial and obligate parasites.
• Asexually they reproduce by biflagellate zoospores.
• Sexual reproduction is oogamy that involves the fusion of male and female gametes to form oospore.
• Oospore undergoes meioses to produce haploid biflagellate zoospores.

Example; Phytophthora infestans(causes potato blight)

Zygomycetes

The group is named zygomycetes because a diploid resting spore called the zygospore is formed during the life cycle.

General Characteristics

• They are mostly saprophytic, some others are parasites on plants and animals.
• The vegetative body is mycelium which is well developed, profusely branched and coenocytic.
• The absence of motile sexual or asexual cells.
• The asexual reproduction takes place by sporangiospores, aplanospores or by conidia.
• Sexual reproduction occurs by conjugation of gametangia resulting in the formation of zygospore.

Examples; Rhizopus, Mucor etc

Ascomycetes

The species of ascomycetes are called the sac fungi because they produce sexual pores within the sac-like vascus.

General Characteristics

• Ascomycetes are mostly terrestrial occurring as saprophytes or parasites.
• They have well-developed, branched, septate mycelium except yeast. Yeast is a unicellular fungus.
• Asexually they reproduce by non-motile spores, conidia, oidia or chlamydospores.
• Sexual reproduction takes place by the fusion of gametangia of opposite mating types.
• There is absence of motile cells.

Examples, Saccharomyces cerevisiae, Penicillium, Aspergillus etc.

Basidiomycetes

The members of basidiomycetes are saprophytic or parasitic. The group is named basidiomycetes as they produce the basidiospores at the club-shaped basidium during sexual reproduction.

General Characteristics

• Mycelium is highly developed, profusely branched and septate.
• The mycelia are differentiated into two mating types; (+ve) and (-ve).
• There are two kinds of mycelium; primary mycelium and secondary mycelium.
• Asexual reproduction takes place by fragmentation, budding, oidia, conidia or chlamydospore.
• The dikaryotic cell is formed during sexual reproduction.
• The absence of motile cell throughout the life cycle.
• Basidiomycetes are the most advanced fungi as their fructifications are often large and prominent.

Examples; Mushrooms, Puccinia, Ustilago etc.

Deuteromycetes(The Imperfect Fungi)

Deuteromycetes compromises more than 17000 species of the diverse habits and habitats. It is considered as an artificial class of fungi.

General characteristics:

• The fungi are saprophytes as well as parasites.Parasitic fungi cause serious diseases to plants, animals including human beings.
• Some of them are unicellular while others are multicellular.
• They reproduce asexually by conidia along with some other types of spores.
• The sexual reproduction is entirely absent.
• The asexual stage or imperfect stage in Deuteromycetes is well defined. But the sexual or perfect stage is absent in life cycle, therefore, they are called 'Fungi Imperfecti'.

Example; Alternaria, Fusarium, Helminthosporium etc.