4 Main Types of fungi
Photo credit: by Vanessa Ryan, Flickr: EOL Images. CC BY-NC-SA
The word fungus usually evokes images of mushrooms and toadstools. Although mushrooms are fungi, the forms that a fungus may take are varied. There are over 100, 000 species of described fungi and probably over 200, 000 undescribed.
Most fungi are terrestrial, but they can be found in every habitat worldwide, including marine (500 spp.) and freshwater environments. Fungi are nonmotile, filamentous eukaryotes that lack plastids and photosynthetic pigments. The majority of fungi are saprophytes; they obtain nutrients from dead organic matter. Other fungi survive as parasitic decomposers, absorbing their food, in solution, through their cell walls.
Most fungi live on the substrate upon which they feed. Numerous hyphae penetrate the wood, cheese, soil, or flesh in which they are growing. The hyphae secrete digestive enzymes that break down the substrate, enabling the fungus to absorb the nutrients contained within the substrate. There are four major groups of fungi: Zygomycota, Ascomycota (sac fungi), Basidiomycota (club fungi), and Deuteromycota (fungi imperfecti).
The fungal group Zygomycota is most frequently encountered as common bread molds, although both freshwater and marine species exist. Most of these live on decaying plant and animal matter found on the substrate. Aquatic species are primarily found in sediments or on algae, but some species are also free floating. A few are found attached to aquatic animals or on decaying leaves. Some are parasites of plants, insects, or small soil animals, while others cause serious infections in humans and domestic animals. They are usually recognized by their profuse, rapidly growing hyphae, but some exhibit a unicellular, yeast-like form of growth. Asexual reproduction is by means of spores produced in sporangia borne on the hyphae. Zygomycota get their name from the production of thick-walled sexual structures called zygosporangia, which can remain dormant for long periods.