What is a Mushroom?

Learn about the strange and wonderful world of Mushrooms, including information on how they’re defined, what they’re made of, and how they’re classified.

Getty Images / Martin Wahlborg

Mushrooms are the fruiting bodies of mycelium, a network of threadlike cells that is the vegetative body of the fungus. I think of mushrooms as temples of sex: ornate and highly organized structures that emerge from (and of) mycelium to create and disperse spores— the analog of our eggs and sperm. Mushrooms arise only when conditions are conducive and when the mycelium recognizes sexual reproduction as a priority for the devotion of energy and resources. Once their spores have been dispersed, the fruiting body withers. Mycelium can persist in its substrate as long as it has adequate resources and is not attacked, eaten, or otherwise destroyed. Depending on the circumstances and species, this can be as short as months or as long as millennia. Meanwhile, most types of mushrooms are evanescent—some emerge, sporulate, and decay within hours. More last a number of days to weeks, and some live for months, years, or even decades.

Taxonomy and Classification of Mushrooms

Fungi are a large and diverse group of organisms that are classified separately from plants, animals, bacteria, and protists, forming their own kingdom. Mushroom-forming fungi exist in two of the seven broad divisions (phyla) of fungi: the Ascomycetes and the Basidiomycetes. Ascomycota, the sac fungi, is a very large and diverse group that includes some mushrooms; however, most Ascomycetes take forms other than mushrooms. The group includes many unicellular yeasts, including Saccharomyces cerevisiae, the species we have to thank for bread, beer, and wine. Many are molds such as Penicillium, Aspergillus, and Fusarium.

While humans have succeeded in cultivating some of the edible and medicinal Ascomycete mushrooms such as morels (Morchella spp.), caterpillar fungus (Cordyceps militaris), and some truffles (Tuber spp.), most of these require advanced techniques, so they will not be the focus of this book. Although many of the techniques presented here can be applied to the cultivation of their mycelium, advanced techniques are required for fruiting them. The phylum Basidiomycota, the club fungi, includes the great majority of mushrooms, such as all the mushrooms with gills, pores, or teeth, and most of the jelly and coral fungi. Nearly all the mushrooms that are grown by humans are in this group, so we will focus on their life cycle and biology.


A Generalized Basidiomycete Mushroom Life Cycle

Spores (center and 12 o’clock) are miniscule propagules. Like sperm and eggs, spores are haploid, containing only half a set of genes (and they lack an embryo, which seeds have). Unlike sperm and eggs, spores can begin to grow without being fertilized by one another.

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