Agaricus bisporus

Common mushroom

Scientific classification
Kingdom:	Fungi
Phylum:	Basidiomycota
Class:	Agaricomycetes
Order:	Agaricales
Family:	Agaricaceae
Genus:	Agaricus
Species:	A. bisporus
Binomial name
*Agaricus bisporus* (J.E.Lange) Emil J. Imbach^[1]

Agaricus bisporus is an edible basidiomycete mushroom native to grasslands in Europe and North America. It has two color states while immature—white and brown—both of which have various names. When mature, it is known as Portobello mushroom.

When immature and white—this mushroom may be known as common mushroom, button mushroom, white mushroom, cultivated mushroom, table mushroom, and champignon mushroom. When immature and brown—this mushroom may be known variously as Swiss brown mushroom, Roman brown mushroom, Italian brown, Italian mushroom, cremini or crimini mushroom, brown cap mushroom, or chestnut mushroom.^[2]

Agaricus bisporus is cultivated in more than seventy countries,^[3] and it is one of the most commonly and widely consumed mushrooms in the world.

Agaricus bisporus
Mycological characteristics
	gills on hymenium
	cap is convex
	hymenium is free
	stipe has a ring
	spore print is brown
	ecology is saprotrophic
	edibility: choice

Taxonomy and naming

The common mushroom has a complicated taxonomic history. It was first described by English botanist Mordecai Cubitt Cooke in his 1871 Handbook of British Fungi, as a variety (var. hortensis) of Agaricus campestris.^[4]^[5] Danish mycologist Jakob Emanuel Lange later reviewed a cultivar specimen, and dubbed it Psalliota hortensis var. bispora in 1926.^[6] In 1938, it was promoted to species status and renamed Psalliota bispora.^[7] Emil Imbach imparted the current scientific name of the species, Agaricus bisporus, after the genus Psalliota was renamed to Agaricus in 1946.^[3] The specific epithet bispora distinguishes the two-spored basidia from four-spored varieties.

Among English speakers, Agaricus bisporus is known by many names. A young specimen with a closed cap and either pale white or light brown flesh is known as a button mushroom or white mushroom. In strains with darker flesh, the immature mushroom is variously marketed as a cremini mushroom, baby portobello, baby bella, mini bella, portabellini, Roman mushroom, Italian mushroom, or brown mushroom. At this stage of maturation, the cap also may begin to open slightly. In maturity, the mushroom is called a portobello.^[8] The French name is champignon de Paris ("Paris mushroom").

The spellings "portobello", "portabella", and "portabello" are all used,^[9] but the first of these spellings is the most common.

Description

Agaricus bisporus, white raw
Nutritional value per 100 g (3.5 oz)
Energy	93 kJ (22 kcal)

Carbohydrates	3.26 g
Sugars	1.98 g
Dietary fiber	1 g

Fat	0.34 g

Protein	3.09 g

Vitamins
Thiamine (B1)	(7%) 0.081 mg
Riboflavin (B2)	(34%) 0.402 mg
Niacin (B3)	(24%) 3.607 mg
Pantothenic acid (B5)	(30%) 1.497 mg
Vitamin B6	(8%) 0.104 mg
Folate (B9)	(4%) 17 μg
Vitamin B12	(2%) 0.04 μg
Vitamin C	(3%) 2.1 mg
Vitamin D	(1%) 0.2 μg

Trace metals
Iron	(4%) 0.5 mg
Magnesium	(3%) 9 mg
Phosphorus	(12%) 86 mg
Potassium	(7%) 318 mg
Sodium	(0%) 3 mg
Zinc	(5%) 0.52 mg

Other constituents
Water	92.45 g
Link to USDA Database entry
Units μg = micrograms • mg = milligrams IU = International units
Percentages are roughly approximated using US recommendations for adults. Source: USDA Nutrient Database

The pileus or cap of the original wild species is a pale grey-brown in color, with broad, flat scales on a paler background and fading toward the margins. It is first hemispherical in shape before flattening out with maturity, and 5–10 cm (2–4 in) in diameter. The narrow, crowded gills are free and initially pink, then red-brown and finally a dark brown with a whitish edge from the cheilocystidia. The cylindrical stipe is up to 6 cm (2⅓ in) tall by 1–2 cm wide and bears a thick and narrow ring, which may be streaked on the upper side. The firm flesh is white although stains a pale pinkish-red on bruising.^[10]^[11] The spore print is dark brown. The spores are oval to round and measure approximately 4.5–5.5 x 5–7.5 μm, and the basidia usually two-spored, although two-tetrasporic varieties have been described from the Mojave desert and the Mediterranean with predominantly heterothallic and homothallic lifestyles, respectively.^[12]^[13]

This mushroom is commonly found worldwide in fields and grassy areas following rain, from late spring through to autumn, especially in association with manure. It is widely collected and eaten, even by those who would not normally experiment with mushroom hunting.^[11]

Similar species

Cultivation history

Agaricus bisporus being cultivated.

The earliest description of the commercial cultivation of Agaricus bisporus was made by French botanist Joseph Pitton de Tournefort in 1707.^[14] French agriculturist Olivier de Serres noted that transplanting mushroom mycelia would lead to more mushrooms.

Originally, cultivation was unreliable as mushroom growers would watch for good flushes of mushrooms in fields before digging up the mycelium and replanting them in beds of composted manure or inoculating 'bricks' of compressed litter, loam, and manure. Spawn collected this way contained pathogens and crops commonly would be infected, or not grow at all.^[15] In 1893, sterilized, or pure culture, spawn was discovered and produced by the Pasteur Institute in Paris, for cultivation on composted horse manure.^[16] Today's commercial variety of the common mushroom originally was a light brown color.

In 1926, a Pennsylvania mushroom farmer found a clump of common mushrooms with white caps in his mushroom bed. As with the reception of white bread, it was seen as a more attractive food item and became very popular.^[17] Similar to the commercial development history of the navel orange and Red Delicious apple, cultures were grown from the mutant individuals, and most of the cream-colored store mushrooms marketed today are products of this 1926 chance natural mutation.

Agaricus bisporus is now cultivated in at least seventy countries throughout the world.^[3] Global production in the early 1990s was reported to be more than 1.5 million tons, worth more than US$ 2 billion.^[18]

Vitamin D

While Agaricus bisporus only contains 16 IU of vitamin D as ergocalciferol (vitamin D2), since it also contains high amounts of ergosterol, after temporary exposure to UV light the ergocalciferol contents increase.^[19]^[20]^[21]

Potential medicinal value

Agaricus bisporus also contains sodium, potassium, and phosphorus,^[22] conjugated linoleic acid,^[23] and antioxidants.^[24] Protocatechuic acid and pyrocatechol also are found in A. bisporus.^[25]^[26]

A mycochemical (2-aminophenoxazine-3-one) in white button mushrooms was shown to have aromatase inhibitor properties in vitro.^[27]^[28]

The table mushroom also has been shown to possess possible immune system enhancing properties. An in vitro study demonstrated that the mushroom enhanced dendritic cell function.^[29]^[30]

Mycochemical research

Some 1990 studies have revealed that compounds in raw A. bisporus—along with some other edible mushrooms—contain hydrazine derivatives, including agaritine and gyromitrin, that have been evaluated for carcinogenic activity.^[31]^[32] In preliminary research during the 1980s, administration of uncooked mushrooms to mice induced a significant increase in the number of bone, stomach, and lung tumours,^[33]^[34] however, research also has noted that when cooked, these compounds were reduced significantly,^[35] and in fact, may provide anti-carcinogenic activity by stimulating apoptosis.^[36]

Nonetheless, according to a scientific publication dated 2010, the available evidence to date suggests that agaritine (a hydrazine) consumed during the consumption of cultivated A. bisporus mushrooms poses no known toxicological risk to healthy humans.^[37]