Mushroom

A mushroom is the fleshy, spore-producing fruiting body of a fungus. It usually grows above ground, on soil or another food source. A toadstool is generally a poisonous mushroom. For mushrooms used in cooking, see Edible mushroom. For other meanings of the word, see Mushroom (disambiguation). For other meanings of "toadstool," see Toadstool (disambiguation).

The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus. The word "mushroom" is most often used for fungi (Basidiomycota, Agaricomycetes) that have a stem (stipe), a cap (pileus), and gills (lamellae) under the cap. The name also describes other gilled fungi, with or without stems, and the fleshy fruiting bodies of some Ascomycota. The gills make tiny spores that help the fungus spread across the ground or the surface where it lives.

Mushrooms that look different from the standard morphology often have their own names, such as "bolete," "truffle," "puffball," "stinkhorn," and "morel." Gilled mushrooms are often called "agarics," after their similarity to Agaricus or their order Agaricales.

Mushrooms grow from underground mycelium and can grow quickly when conditions are good. People use them in many ways. Some are safe to eat and good for you, while others are toxic or have strong effects on the mind. Many have roles in folk medicine, ecology, and industry.

Etymology

For centuries, people used the words "mushroom" and "toadstool" without ever agreeing on exact meanings. In the 15th and 16th centuries, words such as mushrom, mushrum, muscheron, mousheroms, mussheron, or musserouns were used.

The word "mushroom" and its variations may have come from the French word mousseron, which is related to moss (mousse). It is not always clear whether a fungus is edible or poisonous. So a "mushroom" may be safe to eat, poisonous, or not pleasant to eat. The word toadstool first appeared in 14th-century England as a name for a "stool" for toads. It may have suggested a poisonous fungus that is not safe to eat. This idea is still part of the word's meaning today.

Identification

Knowing a mushroom's macroscopic structure helps people tell what is and is not a mushroom. Most are basidiomycetes with gills. Their tiny spores, called basidiospores, form on the gills and fall like a fine powder from under the cap. Each spore is shot off tiny structures called basidia and drops between the gills. If you cut off a cap and place it gill-side-down overnight, it leaves a powdery print that shows the shape of the gills. The color of this spore print helps people sort and name mushrooms. Most prints are white, but they can also be brown, black, purple-brown, pink, yellow, or cream. They are almost never blue, green, or red.

Experts still use methods that have been improved since medieval times and the Victorian era. They also look at mushrooms under a microscope. Amateur and professional mycologists check juices, color changes when a mushroom is bruised, smells, tastes, color, habitat, and season. Tasting and smelling can be risky because of poisons and allergens. Chemical tests are also used for some groups. Finding a mushroom's genus can often be done outdoors with a local field guide. Finding its species takes more effort. A mushroom must grow to full size to show the features needed, because very old mushrooms lose these features and stop producing spores. Beginners have often mistaken water marks on paper for white spore prints, or stains from liquid on lamella edges for colored ones.

Classification

Main articles: Sporocarp (fungus), Basidiocarp, and Ascocarp

Typical mushrooms are the fruit bodies of the order Agaricales. Its type genus is Agaricus, and its type species is the field mushroom, Agaricus campestris. In modern molecularly defined classifications, not every member of Agaricales makes mushroom fruit bodies. Many other gilled fungi, which are also called mushrooms, belong to other orders in the class Agaricomycetes. For example, chanterelles are in the Cantharellales, and false chanterelles such as Gomphus are in the Gomphales. The milk-cap mushrooms (Lactarius, Lactifluus) and the russulas (Russula), along with Lentinellus, are in the Russulales. The tough, leathery genera Lentinus and Panus are among the Polyporales, while Neolentinus is in the Gloeophyllales. The little pin-mushroom genus Rickenella, along with similar genera, is in the Hymenochaetales.

Among the mushrooms in the Agaricales are many common fungi. These include the fairy-ring mushroom, shiitake, enoki, oyster mushrooms, fly agarics and other Amanitas, magic mushrooms like species of Psilocybe, paddy straw mushrooms, and shaggy manes. An unusual mushroom is the lobster mushroom. It is a fruit body of a Russula or Lactarius mushroom that has been changed in shape by the parasitic fungus Hypomyces lactifluorum. This gives it a red color and a shape that looks like a cooked American lobster. Other mushrooms do not have gills, so the word "mushroom" is used loosely for them. A full account of their classification is hard to give. Some have pores underneath, and others, like the hedgehog mushroom and other tooth fungi, have spines. The word has been used for polypores, puffballs, jelly fungi, coral fungi, bracket fungi, stinkhorns, and cup fungi. So "mushroom" is used more for the macroscopic fruiting bodies of fungi, the parts we can see, than for one precise taxonomic group. About 14,000 species of mushrooms have been described.

A mushroom grows from a tiny pinhead called a primordium. It is less than two millimeters wide and is found on or near the substrate. It forms inside the mycelium, a mass of threadlike hyphae. The young mushroom looks like a small egg, called a "button," wrapped in a cottony layer called the universal veil. As the mushroom grows, this veil may leave a cup called a volva at the base of the stalk, or small warts on the cap. A second layer, the partial veil, covers the gills that hold the spores. It may leave a ring, or annulus, on the stalk, as in Amanita, Lepiota, and Cortinarius. The gills can attach to the stalk in different ways. In Agaricus, Amanita, Lepiota, and Pluteus, they do not reach the top of the stalk. In Omphalotus and Pleurotus, they run down the stalk. This is called decurrent.

The stalk, also called the stipe or stem, may sit in the middle of the cap or off to one side, as in Pleurotus and Panus. Some mushrooms have no stalk, such as the shelf-like polypores. Puffballs, truffles, jellies, earthstars, and bird's nests usually have no stalk either. A layer of tiny spore-bearing cells, the hymenium, covers the gills. It also lines the tubes of boletes. Mushroom spores help with identification, since their color, shape, and size can help tell species apart. The cell walls of mushrooms are mostly made of glucans and chitin. Glucans help store energy and give the mushroom its structure.

Growth

Many mushrooms seem to appear overnight, growing or spreading quickly. This is where some common English expressions come from, such as "to mushroom" or "mushrooming" (expanding rapidly in size or scope) and "to pop up like a mushroom" (to appear unexpectedly and quickly). In reality, all mushrooms take several days to form tiny early fruit bodies, called primordia. They can then grow quickly by soaking up fluids.

The cultivated mushroom and the common field mushroom first form a tiny fruiting body, called the pin stage because of its small size. When it grows a little larger, it is called a button. Then the mushroom can quickly pull in water from its mycelium and grow bigger by filling up cells that took several days to form in the primordia. Some mushrooms, like Parasola plicatilis (formerly Coprinus plicatlis), grow overnight and may disappear by late afternoon on a hot day after rain. Others grow slowly, adding material from the edges of the colony or by inserting hyphae. For example, Pleurotus nebrodensis grows slowly. Because people also collect it, it is now critically endangered. Although mushroom fruiting bodies do not last long, the mycelium underneath can live for a very long time. A colony of Armillaria solidipes (formerly known as Armillaria ostoyae) in Malheur National Forest in the United States is estimated to be 2,400 years old, possibly older. It covers an estimated 2,200 acres (8.9 km²).

Nutrition

Brown mushrooms are mostly water, about 92%. They also contain 4% carbohydrates, 2% protein, and less than 1% fat. A 100-gram (3.5 oz) serving of raw brown mushrooms has 22 calories. They are a rich source of several B vitamins, such as riboflavin, niacin, and pantothenic acid. They also provide a lot of selenium (47% of the Daily Value) and copper (56% of the Daily Value). They have a moderate amount of phosphorus, zinc, and potassium (10–15% of the Daily Value). They have little or no vitamin C or sodium.

The amount of vitamin D in a mushroom depends on how it is handled after it is harvested, postharvest. Mushrooms that are exposed to sunlight by accident can gain vitamin D. The US Department of Agriculture found that mushrooms exposed to ultraviolet (UV) light contain large amounts of vitamin D. When UV light hits mushrooms, even after they are picked, a substance in them called ergosterol changes into vitamin D₂. This process is now used on purpose to give fresh mushrooms vitamin D for the functional food market in grocery stores. A safety study found that artificial UV light works just as well as sunlight for making vitamin D in mushrooms. UV light has also been used safely for this purpose in food for a long time.

Human use

Further information: Ethnomycology

Main article: Edible mushroom

Mushrooms are used often in cooking and in many cuisines, especially Chinese, Korean, European, and Japanese. People have eaten them since ancient times. Most mushrooms sold in supermarkets are grown on mushroom farms. The most common one, Agaricus bisporus, is considered safe for most people because it is grown in clean, controlled places. Other grown types include Hericium erinaceus, shiitake, maitake (hen-of-the-woods), Pleurotus, and enoki. China grows about half of all cultivated mushrooms. In 2014, Poland was the world's largest mushroom exporter.

Telling edible mushrooms from poisonous ones takes great care, because no single feature tells you whether a mushroom is safe. People who collect mushrooms to eat are called mycophagists. The activity is called mushroom hunting, or "mushrooming". Even edible mushrooms can cause allergic reactions, from a mild asthmatic response to a severe anaphylactic reaction. The cultivated A. bisporus contains small amounts of hydrazines, and the most common one is agaritine, which is a mycotoxin and carcinogen. Cooking with moderate heat destroys hydrazines. Some poisonous mushrooms look like edible ones, and eating them can be deadly. For this reason, wild mushrooms should only be eaten by people who know how to identify them. A common rule is that if a mushroom cannot be clearly identified, it should not be eaten.

In Jainism, eating mushrooms and other edible fungi is strictly forbidden. This rule comes from the religion's core belief in nonviolence (ahimsa). Classical Jain thinking describes mushrooms as ananthkay, bodies that hold an endless number of tiny souls or lifeforms (nigoda). They are also seen as places where moving microorganisms (trasa jiva) can grow.

Many mushroom species make secondary metabolites that can be toxic, change how the mind works, fight germs, or bioluminescent, meaning they glow. Only a small number are deadly species, but several others can cause serious and unpleasant symptoms. Toxicity may help protect the mushroom's spore-producing structure. Some chemicals make a mushroom unpleasant to eat by causing vomiting (see emetics) or by teaching animals to avoid it. Because mushrooms can absorb heavy metals, European mushrooms were found to carry contamination from the 1986 Chernobyl disaster as late as 2008, and scientists have continued to study them.

Mushrooms with mind-altering properties have long been part of traditional medicine around the world. They have been used in ceremonies for healing and spiritual experiences, such as the velada ceremony, led by a shaman or curandera (priest-healer).

Psilocybin mushrooms, also called psychedelic or "magic mushrooms", have psychedelic properties. They are sold openly in smart shops in many parts of the world, or illegally on the black market where sale is banned. People have reported mystical experiences after taking them, and recent scientific work has supported some of these reports.

Psilocybin, found in psychedelic mushrooms such as Psilocybe cubensis, is being studied as a possible help for people with conditions such as obsessive–compulsive disorder. Small amounts have been reported to help stop cluster and migraine headaches. A careful study by Johns Hopkins Hospital found that psychedelic mushrooms could lead to an experience with deep personal meaning. Many of the people in the study said that taking them was one of the most spiritually important moments of their lives. Psilocybin mushrooms have also shown promise in helping people with addictions to alcohol and cigarettes.

A few species of Amanita, most notably A. muscaria and A. pantherina, contain the mind-altering compound muscimol. These species do not contain amatoxins or phallotoxins, so they do not harm the liver in the same way. However, if they are not properly cured, they can cause non-deadly harm to the nervous system because of ibotenic acid/ibotenic acid. In high doses, the effects can include dissociation and delirium. A third type is the hallucinogenic bolete mushrooms, such as Lanmaoa asiatica, which are said to cause Lilliputian hallucinations. Scientists do not yet know their active ingredients, and they are still being researched.

Some mushrooms are used in folk medicine. Further information: Medicinal uses of fungi

In a few countries, extracts such as polysaccharide-K, schizophyllan, polysaccharide peptide, or lentinan are registered by the government as adjuvant cancer therapies. However, scientists have not yet confirmed that they are safe or that they work in people. The US Food and Drug Administration treats this use as a dietary supplement. That means it does not have government approval or common medical use as a prescription drug.

Mushrooms can be used for dyeing wool and other natural fibers. The chromophores in mushroom dyes are compounds that produce strong, bright colors. Before synthetic dyes were invented, mushrooms were the source of many fabric dyes. Some polypores, which are loosely called mushrooms, have been used as fire starters, known as tinder fungi. Mushrooms and other fungi also help scientists develop new ways to clean up pollution, such as using mycorrhizae to help plants grow, and new filtering technologies. Researchers are also studying genetic engineering to improve mushrooms for food and medicine.