Fungi are mainly classified into following four types :
I. PHYCOMYCETES (ALGAE - FUNGI )
Phycomycetes include the simplest type of fungi. This group is also called as Algae-Fungi because most of the characteristics of this group are similar with algae like Vaucheria . Fungi belonging to this class are either aquatic or terrestrial. They may be obligate parasites on plants or saprophytic as they grow on decaying wood in damp and moist places.
GENERAL CHARACTERS :
1. They have simple coenocytic or aseptate mycelium.
2. They reproduce asexually by motile zoospores or non-motile aplanospores endogenously produced in sporangium.
3. Sexual reproduction is isogamous or heterogamous that takes place by gametangial copulation.
4. Two types of flagella (whiplash and tinsel type) are present in phycomycetes.
5. The diploid phase is represented by the zygote.
Examples: Mucor, Rhizopus and Albugo (the parasitic fungi on the members of family Brassicaceae like mustard).
Phycomycetes has been classified into two sub-classes: Oomycetes and Zygomycetes :
GENERAL CHARACTERS OF OOMYCETES ( water moulds or egg fungi ) :
1. Most of them are parasitic to plants.
2. Mycelium is commocytic
3.Hyphal wall contains cellulose and chitin along with glucans.
4. Formation of biflagellated zoospores takes place.
5. Oospore (2n) is formed after fertilization. 6. Gametes are non-flagellate.
7. Sexual reproduction is by gametangial contact, in which male sex-organ antheridium passes its contents into female sex-organ oogonium.
8. The fusion of male and female gametes produce oospore eg. Phytophthora infestans, Albugo candida.
GENERAL CHARACTERSTICS OF ZYGOMYCETES ( the conjugation fungi )
1.They are mostly saprophytes, rarely parasites.
2. Mycelium is coenocytic.
3. Hyphal wall contains chitin or fungal cellulose.
4. Motile cells are absent.
5. Asexual reproduction takes place by sporangiospores which are formed in the sporangia, borne tips of sporangiophores.
6. Sexual reporduction occurs by gametangial copulation or conjugation.
7. Gametes are multinucleate.
8. Sexual reporduction produces resting diploid spores, called zygospores (2n).
9. Zygospore dose not directly give rise to mycelium. It produces germ-sporangium, inside which meisopores called germ spore are formed. The germ spores germinate into mycelium. eg. Rhizopus , Mucor , Pilobolus.
II . ASCOMYCETES ( also sac fungi because they bear spores in sac like structure called ascus )
1. It includes diverse group of fungi (over 30,000 sp) appearing in various pigmented moulds ,powdery mildews , yeasts , cup fungi , morels and .truffles .
2. Mycelium consists of septate hyphae but yeasts are unicellular.
3. Septa possess central septal pores.
4. Cell wall contains chitin.
5.Asexual reproduction takes place by conidia. Budding (in yeast) or oidia is also found in some case
6.Sexual reproduction takes place by gametangial copulation or gametangial contact.
7. Ascus is sporangial sac. 4-8 haploid ascospores are produced in each ascus. Half number of ascospores belongs to one mating type (+ve) and next half to other mating type (-ve).
8. Asci may occur freely or get aggregated into specific fructification called ascocarp. Ascocarps are of different shapes, cup like (apothecium, eg. Peziza), flask-shaped (Perithecium, eg. Neurospora), elongated with a slit (hysterothecium) or closed (Cleistothecium) eg. Penicillium.
9. Ascomycetes are mostly terristerial which maybe saprophytes or parasites .
III. BASIDIOMYCETES ( the club fungi )
General characters :
1. They have highly developed, profusely branched and septate mycelium. The septa have either micropore or simple pores (dolipore).
2. There are two kinds of mycelium: primary mycelium and secondary mycelium.
3. The mycelia are well differentiated into two mating types: (+ve) and (-ve).
4. They reproduce by vegetative, asexual and sexual methods.
5. Asexual reproduction takes place by fragmentation, budding, oidia, conidia or chlamydospore.
6. The dikaryotic cell (n+n) is formed during plasmogamy of sexual reproduction.
7. The flagellate or motile cells are absent throughout the life cycle.
8. Basidiomycetes are the most advanced fungi because their fructifications are often large and prominent. Examples: Mushrooms, Puccinia (Rust), Ustilago (smut) etc.
IV . DEUTEROMYCETES (The fungi imperfectii )
The fungi belonging the Deuteromycetes are known as fungi imperfecti or asexual fungi or mitosporic fungi because they reproduce asexually by conidia formation, but the perfect stages or sexual reproduction is completely unknown. Therefore, the class deuteromycetes is also considered as an artificial class of fungi. They are found in diverse habits and habitats.
1. The vegetative body is well-developed septate; profusely, branched hyphae, is called mycelium. septa between the adjacent hyphal cells have pores, called dolipores.
2. The hyphal cells are multi-nucleate and hyaline in colour.
3. The fungi are saprophytes as well as parasites, Parasitic fungi cause serious diseases to plants, animals including human beings.
4.Some of them are unicellular while others are multicellular.
5.A few fungi produce appressoria and haustoria .
6. They reproduce asexually by conidia along with some other types of spores like chlamydospores.
7. Generally, conidia are produced externally on conidiophores arising directly from the vegetative mycelium. Sometimes, conidiophores are produced in special fruiting bodies like pycnidia, synnemata or acervuli .
8.The sexual reproduction is entirely absent.
9.The asexual stage or imperfect stage in deuteromycetes is well defined. But the sexual or perfect stage is absent in the life cycle, therefore, they are called 'Fungi Imperfecti'.
Example: Alternaria, Fusarium, Helminthosporium, etc.