Cultivated Mushroom

Description

The cultivated mushroom is the well-known button mushroom from shops: white or brown, with a fleshy cap 4–10 cm across, gills that turn pink and then dark brown, and a distinct ring on the stem. The flesh is white, firm, with a mild smell, and turns slightly red when damaged.

In the wild it is rare: it grows on rich soil, compost and manure, in fields, parks and on compost heaps. On the other hand, it is cultivated on a huge scale, and Poland is the largest producer of button mushrooms in Europe. Collecting wild specimens is not recommended because they are easy to confuse.

The greatest danger is confusion with young, deadly poisonous amanitas, which have white gills and a volva at the base of the stem, and with the inedible yellow stainer, which turns yellow and smells of phenol. If you are not sure of the species, do not pick or eat it.

Identification features

Cap

Diameter 4–10 cm (mature portobello 10–15 cm). Hemispherical when young, then flattened. Colour white, greyish-white to brownish; the wild form is light grey-brown with broad flat scales on a paler background, paler towards the margin. Cap skin radially fibrillose to adpressed-scaly. Cap thick and fleshy.

Hymenophore (underside of the cap)

Gills free, narrow, crowded; whitish in young fruiting bodies, then pink, finally dark brown, with a whitish edge (cheilocystidia).

Stem

Height 3–8 cm, thickness 1–3 cm (descriptions give different ranges); cylindrical, solid, white, sometimes scaly below the ring. Ring distinct, thick, narrow, sometimes striate on the upper side. No volva at the base.

Flesh

White, firm, weakly reddening when damaged (pale pinkish-red). Smell faint, pleasant. It does not turn yellow when damaged — yellowing and a phenol smell indicate the yellow stainer. Do not taste wild specimens.

Spore print and spores

Spore print brown to dark brown. Spores ellipsoid to roundish, smooth. Size about 4.5–8.5 × 4–7.5 µm (descriptions give different ranges). Basidia usually two-spored (four-spored varieties have also been described).

Habitat and distribution

Ecology. Terrestrial saprotroph on rich soil, compost and manure; rare in the wild, in fields, parks, compost heaps and fertilised places, rarely in forests. Cultivated on compost (in Europe mainly on horse manure).

Distribution. In the wild: North, Central and South America, Europe, Asia, Australia and numerous islands. In Poland the distribution and frequency of wild populations are unknown (5 localities were reported up to 2003). Cultivated in more than 70 countries. Poland is the largest producer of button mushrooms in Europe. It is not legally protected; it appears on the list of fungi approved for sale (Ministry of Health item 38; in the catalogue it also covers A. hortensis).

Fruiting. From May to September; according to some descriptions it fruits from autumn to winter, especially near cypresses. Cultivation is year-round.

What can it be confused with?

• Agaricus xanthodermus (yellow stainer) — Inedible, causes stomach upset; smells of phenol (carbolic acid), and the flesh, especially at the base of the stem, turns yellow when damaged.
• Agaricus campestris (field mushroom) and Agaricus arvensis (horse mushroom) — The cultivated mushroom has the thickest, most fleshy cap. Young specimens can be reliably distinguished only under the microscope.
• Amanita virosa and other deadly poisonous amanitas (destroying angels) — Young specimens may look similar, but amanitas have a volva at the base of the stem and pure white gills, whereas the mushroom has pink or brown gills and a brown spore print.
• Entoloma sinuatum — Gills yellowish, turning pink; no ring.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• The white button mushroom arose in 1925 as a spontaneous mutation on a farm in Coatesville (Pennsylvania); most of today's white button mushrooms descend from that single clone.
• In 2012 French scientists from INRA in Nancy sequenced the genome of the species.
• Poland is the largest producer of button mushrooms in Europe (about 330,000 tonnes a year) and the largest exporter of these mushrooms in the world.
• The first scientific description of mushroom cultivation comes from Tournefort in 1707; in 1893 the Pasteur Institute produced sterile mycelium.