Based on the morphology of mycelium, mode of nutrition, mode of spore formation and fruiting bodies, the kingdom Fungi is divided into 4 classes- Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes.
Phycomycetes: They are called lower fungi and occur in water, on decaying wood and leaves in moist and damp places and also as parasites on plants. Mycelium is coenocytic and aseptate. Asexual reproduction byzoospores in aquatic forms and aplanospores in terrestrial forms. Sexual reproduction is by isogamy, anisogamy and oogamy.
Example: Mucor, Rhizopus, Albugo etc.
Ascomycetes: They are higher fungi with a well-developed thallus and productions of ascospores within the sac like ascus.They are also called sac fungi. Ascomycetes are unicellular or multicellular. The hyphae are septate and each cell may be uninucleate or multinucleate. Asexual reproduction by conidia and sexual reproduction by the fusion of two hyphae of different mating types.
Examples: Yeast, Penicillium, Aspergillus, Claviceps, Morchella etc.
Basidiomycetes: They grow in soil, on logs,and tree stumps and as parasites in living bodies. Vegetative reproduction by fragmentation. Asexual and sexual reproductions are absent. Mycelium is septate, multinucleated and branched.
Example: Agaricus, Ustilago, Puccinia etc.
Deuteromycetes: They are also called imperfect fungi or fungi imperfecti.It is an artificial group of fungi which includes the fungi having only the asexual reproduction. Majority of the members are haploid and possess a septate branched mycelium. They are parasites or saprophytes. They cause a variety of diseases in plants, animals and man.
Examples: Cercospora, Alternaria, Fusarium, Colletotricum, Trochoderma etc.