Classification of fungi
The phylum Chytridiomycota, the chytrids, represents a group of primitive aquatic fungi. They are characterized by having gametes that are motile by means of flagella.
The zygomycetes, in phylum Zygomycota, are characterized by the formation of sexual spores called zygospores. The zygospores are not contained within a specialized fruiting body or sac. Zygospores form when the haploid nuclei at the ends of two hyphae fuse together in a process of fertilization to form a diploid zygote. The zygote immediately undergoes meiosis to form haploid cells that develop into zygospores. The zygospores are unenclosed, or “naked,” between the parental hyphae. An example of a zygomycete is the common black bread mold, Rhizopus nigricans.
The ascomycetes are members of the phylum Ascomycota. They are also called the “sac fungi” because their sexual spores (ascospores) are enclosed in tube-like sacs known as asci. The formation of ascospores is similar to that of zygospores, except that the ascospores formed by meiosis are enclosed in the asci. Neurospora crassa is an ascomycete mold that was important in studies of genetic linkage.
Basidiomycetes, also known as the “club fungi,” are classified in phylum Basidiomycota. Their sexual spores, or basidiospores, are formed on complex fruiting body structures called basidia. Basidiomycetes include some of the most complex fungi, including mushrooms and puffballs.
The group known as deuteromycetes are also called the “imperfect fungi.” This group contains species for which no sexual stage has been discovered. At one time, many of the parasitic fungi were classified into this group. However, many of these species have recently been reclassified into one of the other phyla when the sexual stage was discovered. An example of a deuteromycete is Candida albicans, a dimorphic fungus responsible for “yeast infections” in humans.
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