A mushroom typically consists of a stalk (stipe) and a cap (pileus). As the mushroom develops from …—© Merriam-Webster Inc.

Fleshy spore-bearing structure of certain fungi (see fungus), typically of the phylum Basidiomycota. It arises from the mycelium, which may live hundreds of years or a few months, depending on its food supply. Some species grow cellular strands (hyphae) in all directions, forming a circular mat with a “fairy ring” of fruiting bodies around the outside. Popularly, “mushroom” refers to the edible sporophores, while “toadstool” refers to inedible or poisonous sporophores, but there is no scientific distinction between the two names. Umbrella-shaped sporophores with spore-shedding gills on the undersurface are found chiefly in the agaric family (Agaricaceae). Mushrooms that are cap-shaped and bear spores in an easily detachable layer on the underside of the cap belong to the family Boletaceae. Together the agarics and boletes include most of the forms known as mushrooms. The morels (phylum Ascomycota) are popularly included with the true mushrooms because of their shape and fleshy structure. Since some poisonous mushrooms closely resemble edible ones, mushrooms intended for eating must be accurately identified. Mushroom poisoning can cause nausea, diarrhea, vomiting, cramps, hallucinations, coma, and sometimes death.

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