What is a Mushroom?

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Mushrooms are the fruiting bodies produced by some fungi. Not all fruit bodies are true mushrooms. Puffballs and morels are edible fruit bodies that are sometimes called "mushrooms". The function of this visible part of some fungi is to produce and disperse the largest possible number of spores in the shortest possible time. Spores create new individuals after being carried away on the wind and landing in a good place for growth.

True mushrooms typically look like umbrellas. They consist of a stalk topped by a flat or cup-shaped cap. Their spores are produced on special cells called basidia, located on the underside of the cap. The class of fungi whose spores are produced by basidia are called Basidiomycetes.

People often ask about the difference between toadstools and mushrooms. Any mushroom can be called a toadstool, but this word usually refers to a poisonous mushroom.

What do they look like?

Click the link to see some photographs of mushrooms with gills and mushrooms without gills.

Life History of Mushrooms

While mushrooms may seem to sprout overnight, it actually takes days or weeks for one to develop. Most of the growth of a fungus goes unnoticed because it occurs underground. The underground body of a fungus, called the mycelium, is made of moist thread-like filaments called hyphae. When growing conditions are good, little knots of hyphae called primordia are formed. As individual primordia grow larger, the hyphae within them organize into two parts. One part will become a mushroom’s cap, and the other, its stem.
mushroom growth animation

When the primordium gets large enough, the stem elongates and pushes the cap up above the ground. As the stem elongates, the cap expands, a little like an umbrella unfolding. In some mushrooms, the expanding cap breaks a veil-like membrane extending from the cap to the stem, leaving a ring. Some growing mushrooms may also break a second membrane that covers it completely, and dried bits of this broken veil form scales on the cap.
Parts of Mushroom

On the underside of the cap, the spore-producing basidia are found in several different structures. Basidia may cover the surface of tissue-thin hanging plates called gills, or line the inside of tubes, or cover "teeth".

Basidia produce four spores at the end of microscopic spines called sterigma. When the spores are ready, they are discharged a short distance into the space between the gills or teeth, or into the center of the tube. The spores then fall out of the cap and are carried away in the wind. Most spores land within three feet (1 m) of the mushroom that produced them, but they can be carried much further. If the spore lands in a good spot, it germinates, producing the mycelium of a new fungus individual.
basidium animation

The puffballs are relatives of mushrooms whose basidia and spores are enclosed in a sac instead of covering gills, or in tubes. Coral fungi are also mushroom relatives. They produce branched fruiting bodies that resemble coral or broccoli.

Despite producing large mushroom-like fruiting bodies, morels and false morels are not closely related to mushrooms. These fungi are related to the cup fungi, in the class Ascomycetes. Their spores are produced inside a special cell called the ascus, instead of on the outside of basidia. The spores of morels and false morels are explosively discharged into the air as a fine white cloud.