Field Mushroom

Description

The field mushroom is a white or greyish-ochre agaricus with a cap 5–11 cm across, silky fibrous, often cracked in dry weather. The gills are pink, then chocolate-brown to black, and the white, thin ring on the stem is often not persistent. The flesh is white and turns pink in places when cut.

It grows from May to October in meadows, pastures, lawns and fields, especially where there is manure. After warm rains the fruiting bodies can shoot up within a single day. The Polish saying "to grow like mushrooms after the rain" is linked to its appearance. Because of overly intensive fertilisation of meadows there is less and less of it.

The most dangerous mistake is confusing very young, white-gilled specimens with the deadly poisonous destroying angel; the amanita has a volva at the base of the stem and always white gills. Such poisonings have occurred, also in France. Also distinguish it from the yellow stainer, which turns yellow and smells of phenol. At the slightest doubt, do not pick or eat it. Do not pick from lawns exposed to pesticides either.

Identification features

Cap

Diameter 3–12 cm (descriptions give different ranges). Young closed, almost spherical, then hemispherical, finally spread flat. Margin scaly-cracked, surface silky fibrous, with sparse, adpressed brown scales at the top. Colour initially white, later greyish-ochre. In dry weather the upper surface cracks into patches. The skin peels off easily. Turns yellow or brown when pressed (older specimens).

Hymenophore (underside of the cap)

Gills crowded, free from the stem. White only in very young, closed fruiting bodies; they quickly become pink, then increasingly dark: chocolate-brown to blackish-brown, violet-black from spores in old ones.

Stem

Height 4–8 cm, thickness 1–2 cm, cylindrical, solid, easily detached from the cap. White membranous ring high on the stem, not very persistent, disappearing in older specimens (according to some descriptions single, thin). Surface smooth, white, brownish in older ones; the upper part is often pinkish. Base of the stem without a volva.

Flesh

White or watery pink, turning pink in places when cut (according to some descriptions dirty reddish-brown, unlike the yellow stainer, in which it turns yellow). Above the gills often a grey tinge, orange at the base of the stem. Taste pleasant, mild, smell slightly mushroomy.

Spore print and spores

Spore print blackish-brown to dark brown. Spores ellipsoid, smooth, thick-walled. Size 5.5–10 × 4–6 µm (descriptions give different ranges).

Habitat and distribution

Ecology. Terrestrial saprotroph in meadows, pastures, lawns, roadside ditches and fields, most often on moderately fertilised places (e.g. where cattle graze), and it especially likes horse manure. Rarely in forests. Grows singly, in small groups or in fairy rings.

Distribution. On all continents except Antarctica, also on many islands. In Central Europe it is widespread and fairly common, but its numbers are declining because of excessive fertilisation of meadows. It is not legally protected in Poland; it appears on the list of fungi approved for sale (Ministry of Health item 41). The fruiting bodies grow very quickly after heavy rain.

Fruiting. From May to October (according to some descriptions from late summer).

What can it be confused with?

• Amanita virosa (destroying angel), Amanita hygroscopica and other deadly poisonous amanitas — Fatal mistakes concern especially very young, closed fruiting bodies with still white gills. Amanitas always have white gills, a whitish spore print and a stem surrounded by a volva at the base; agaricus mushrooms have gills that quickly turn pink and a brown spore print. It is advisable to examine the whole base of the stem and neighbouring young fruiting bodies.
• Agaricus xanthodermus (yellow stainer) — Inedible, causes stomach problems; the flesh turns yellow when damaged (especially at the base of the stem), the smell resembles phenol.
• Agaricus arvensis (horse mushroom) — Often grows outside forests, ring on the stem with scales, aniseed or almond smell, gills mature through pale greyish-pink.
• Agaricus bitorquis (pavement mushroom) — Cap always bare and a double ring on the stem.
• Agaricus bisporus (cultivated mushroom) — Young specimens are hard to tell apart; the place of origin (cultivated) helps, the microscope distinguishes them reliably.
• White Clitocybe (funnel caps) on lawns — May be toxic; they have a pale spore print and decurrent gills.

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

• It is this fast-growing field mushroom that supposedly gave rise to the saying "to grow like mushrooms after the rain".
• Polish Post issued a stamp with this species on 8 May 1959 (the "Mushrooms of Poland" series, face value 2.50 zł, withdrawn from circulation on 31 December 1994) and again on 29 August 2014 (2.35 zł).
• The former "white fields" of field mushrooms are becoming rare because there are fewer horses on pastures.
• The species was described by Linnaeus in 1753; the epithet campestris means "of the field".