Agaricus bisporus

Common mushroom
Scientific classification
Kingdom:	Fungi
Division:	Basidiomycota
Class:	Agaricomycetes
Order:	Agaricales
Family:	Agaricaceae
Genus:	Agaricus
Species:	A. bisporus
Binomial name
Agaricus bisporus (J.E.Lange) Imbach (1946)
Synonyms
Psalliota hortensis f. bispora J.E.Lange (1926)

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

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, often shortened to just portobello.

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.

A. bisporus is cultivated in more than seventy countries, and is one of the most commonly and widely consumed mushrooms in the world.

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. Danish mycologist Jakob Emanuel Lange later reviewed a cultivar specimen, and dubbed it Psalliota hortensis var. bispora in 1926. In 1938, it was promoted to species status and renamed Psalliota bispora. Emil Imbach imparted the current scientific name of the species, Agaricus bisporus, after the genus Psalliota was renamed to Agaricus in 1946. The specific epithet bispora distinguishes the two-spored basidia from four-spored varieties.

Among English speakers, A. 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. The French name is champignon de Paris ("Paris mushroom").

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

Description

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 (2.0–3.9 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 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. 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.

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.

Similar species

See also: Mushroom hunting

The common mushroom could be confused with young specimens of the deadly poisonous destroying angel (Amanita sp.), but the latter may be distinguished by their volva or cup at the base of the mushroom and pure white gills (as opposed to pinkish or brown of A. bisporus). Thus it is always important to clear away debris and examine the base of such similar mushrooms, as well as cutting open young specimens to check the gills. Furthermore, the destroying angel grows in mossy woods and lives symbiotically with spruce.

A more common and less dangerous mistake is to confuse A. bisporus with Agaricus xanthodermus, an inedible mushroom found worldwide in grassy areas. A. xanthodermus has an odor reminiscent of phenol; its flesh turns yellow when bruised. This fungus causes nausea and vomiting in some people.

The poisonous European species, Entoloma sinuatum, has a passing resemblance as well, but has yellowish gills turning pink and it lacks a ring.

Cultivation history

File:Agaricus bisporus mushroom.jpg

A. bisporus being cultivated.

The earliest description of the commercial cultivation of A. bisporus was made by French botanist Joseph Pitton de Tournefort in 1707. 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. In 1893, sterilized, or pure culture, spawn was discovered and produced by the Pasteur Institute in Paris, for cultivation on composted horse manure.

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. 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.

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

Nutritional profile

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
Minerals
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

In a 100 gram serving, raw white mushrooms provide 22 calories and are an excellent source (> 19% of the Daily Value, DV) of the B vitamins riboflavin, niacin, and pantothenic acid (table). Fresh mushrooms are also a good source (10–19% DV) of the dietary mineral, phosphorus (table).

While fresh A. bisporus only contains 0.2 micrograms (8 IU) of vitamin D as ergocalciferol (vitamin D2), the ergocalciferol content increases substantially after exposure to UV light.

Research

Mushrooms contain hydrazine derivatives, including agaritine and gyromitrin, that have been evaluated for carcinogenic activity. Agaritine, a hydrazine, poses no toxicological risk to humans when mushrooms are consumed in typical amounts.

Gallery

• Portobello mushrooms.jpg

  Portobello mushrooms

• Giant mushroom cross-section.jpg

  Cross-section of a portobello cultivar

• Giant mushroom underside.jpg

  Ventral view of a portobello cultivar with a bisected stipe

• Agaricus bisporus (Cup mushroom, doubled).jpg

  Two Agaricus bisporus mushrooms which have fused together

• Agaricus bisporus Zuchtchampignon2.jpg

  White Agaricus bisporus

• 2014 11 Portobello rocket feta toasted baguette.jpg

  Grilled portobello, feta, and rocket salad on toasted baguette

See also

• Effect of sunlight on mushrooms
• Fungiculture
• List of Agaricus species
• Medicinal mushrooms