The study of fungi (s. fungus) is called mycology. Fungi are unicellular or multicellular chemoheterotrophic eukaryotes. They may be grouped into yeasts, molds and fungal-like agents. Yeasts are oval to spherical single cells; they reproduce by budding. Molds are multicellular filamentous fungi that consist of thread like filaments called hyphae (s. hypha) that grow by elongation of their tips into an intertwining mat called the mycelium (pl. mycelia). Hyphae may be septate or non septate (example: mucor, rhizopus, absidia) Fungal-like agents, viz. Prototheca and Pythium species are discussed traditionally as mycotic agents since they produce elements that resemble fungi in tissue, and some may form yeastlike colonies on mycological media. The cell wall of fungi contain cellulose, chitin, glucan, chitosan or mannan. The mode of reproduction is by means of specialized cells, called spores. The fungi can be divided into the following four morphological groups:
(i) the moulds which are filamentous
(ii) the yeasts are unicellular and reproduce by budding
(iii) the yeast like fungi, partly grow as yeasts and partly as long filaments
(iv) the dimorphic fungi grow either as filaments or as yeasts, pending on cultural conditions.
Pathogenic fungi are categorized into groups based on sexual reproduction. These comprise ascomycetes, basidiomycetes, zygomycetes and deuteromycetes (fungi imprfectii).