Fungi are classified based on their mode of reproduction:
Zygomycota: The zygomycetes are coenocytic fungi that form thick walls around the diploid zygote. When hyphae from two different mating types come in contact with each other, they form gametes which then fuse to form a zygospore (see Figure 9.3). When nuclear fusion occurs, the diploid zygote goes through meiosis and produces haploid spores, which are then dispersed and can germinate to form new mycelium under appropriate conditions. The black bread mold Rhizopus stolonifer is an example of this group.
Ascomycota: Also known as the sac fungi, ascomycota form saclike structures called asci (singular ascus) during sexual reproduction (see Figure 9.4). The asci produce haploid spores that are eventually dispersed. During asexual reproduction, spores, called conidiospores, are produced at the end of hyphae. Truffles, fermenting yeast (Saccharomyces cerevisiae) and the bread mold Neurospora crassa are examples of this group.
Basidiomycota: The fungi in this group form basidia, club shaped, spore producing structures (i.e. mushrooms). For this reason, the Basidiomycota are also called club fungi. This is the largest and most diverse group of the fungi. There is no asexual reproduction in these fungi. The hyphae of different mating types will conjugate to form mycelium containing two different nuclei. The mycelia produce basidia. Nuclear fusion occurs in the mushroom bodies to produce diploid cells that go through meiosis to produce haploid spores. These spores can then be dispersed to produce new mycelium.
Deuteromycota: These fungi are classified as imperfect fungi, as they have no sexual reproduction phase that can be identified. In many cases, once a mode of sexual reproduction has been determined, a species will be reclassified to one of the other groups. One example of an imperfect fungus is Penicillium, the organism that produces penicillin.
Lichens: One last classification of fungi is the lichens. Lichens are two different species that interact: one species is a fungus and the other a photosynthetic organism, such as algae.