The final division in the kingdom Fungi that we will cover is the phylum Basidiomycota. This is the phylum that you are probably most familiar with because it contains fungi which are generally referred to as gilled fungi or gilled mushrooms. However, with over 25,000 classified species, it also houses diverse members such as puffballs, shelf fungi, and rusts (which are important plant pathogens). Basidiomycetes are often called club fungi because the cells (basidia ) that bear the sexual spores resemble a small club. Biologically, basidiomycetes follow the same theme as the rest of the fungal kingdom; they are important decomposers, plant pathogens, and symbionts with plants (mycorrhizal). In particular, basidomycetes excel at breaking down large plant cell wall polymers (e.g., lignin found in decaying wood). Morphologically, they range in complexity from microscopic single cells to conspicuous fruiting bodies called basidiocarps . A mushroom that you are likely to see in a forest or at the grocery store is a basidiocarp. Produced during its sexual cycle, it can bear millions of spores on club-shaped basidia located on the surface of its gills. The production of gills underneath the cap is an adaptation that provides a large surface area for spore production. Amazingly, the surface areas on the gills of a store-bought button mushroom could cover the surface of a large trash can lid. This is an example of a highly evolved, morphological feature of gilled fungi. The gills are protected by the top of the cap and elevated by the stem of the basidiocarp for efficient wind dispersal of its basidiospores . Basidiomycetes have also developed unique methods for spore dispersal. Some species produce their spores on basidia in a slimy mass that emits an odor similar to rotting carrion. Flies are attracted to the smell and, in doing so, become agents of spore dispersal.
Although some basidiomycetes produce asexual spores, asexual reproduction is far more common in the phylum Ascomycota. Therefore, we will discuss a generalized life cycle covering sexual reproduction. Turn your attention to the basidiomycete life cycle.
In steps 1 and 2, two haploid hyphae of opposite mating types fuse to produce a dikaryotic hypha. In step 3, under favorable environmental conditions (optimum temperature and moisture levels), the dikaryotic hypha is capable of producing a fruitbody; in this case, a gilled mushroom. In step 4, basidia begin to form on the surface of the gills, and in step 5, karyogamy occurs to form a diploid nucleus in each basidium. In step 6, meiosis immediately follows karyogamy and each of four genetically distinct, haploid nuclei migrates into appendages and develops into basidiospores. Basidiospores are released and wind dispersed. They germinate into haploid hyphae and the cycle begins again in step 7.