Yellow-stainer

Description

The yellow-stainer (pieczarka karbolowa) looks like an ordinary field mushroom: it has a white, silky cap 4–12 cm across, a white, slender stem with a bulbous base and a hanging ring. The gills are at first pink, then chocolate-brown. The most important feature is the intense, chrome-yellow staining after scratching or cutting the base of the stem, and the smell of carbolic acid or ink, strongly intensifying during cooking.

It grows from May to October on lawns, in parks, gardens, by roads and in forests. In Poland it is fairly frequent and is sometimes the cause of poisonings, because it is easily confused with mushrooms, especially the horse mushroom and the field mushroom.

The rule of recognition by smell applies only to agarics; many other poisonous mushrooms cannot be told apart by smell. If you are not certain of the species, do not collect or eat it.

Identification features

Cap

Diameter 4–12 (15) cm, convex when young, sometimes almost square, then flattened. Colour white, the top often pale beige or pale brown. Skin silky, dry, smooth, often cracking radially, scaly in older ones. Turns yellow under pressure or when scratched.

Hymenophore (underside of the cap)

Gills fairly thin, free; at first pink or pinkish-whitish, chocolate-brown with age.

Stem

Height 5–12 cm, thickness 1–3 cm, white, slender, bulbous towards the base, sometimes hollow inside. Ring hanging, skirt-like, with a characteristic edge running all the way round on the underside. Turns chrome-yellow under pressure and at the base.

Flesh

White; when cut, especially at the base of the stem, it immediately turns an intense yellow (chrome-yellow) colour, which later fades to dull brown. Smell phenolic, described as carbolic or inky, sickly sweet, strongest at the base of the stem and greatly intensifying during cooking. Taste very unpleasant — it must not be tasted; do not taste the flesh of this or any suspicious mushroom.

Spore print and spores

Spore print dark, brown. Spores ellipsoid, smooth: 5.5–7 × 3–4.5 µm (descriptions give different ranges).

Habitat and distribution

Ecology. Terrestrial saprotrophic fungus. Grows in deciduous and coniferous forests, by roads and in roadside scrub, in parks, gardens, on lawns and meadows, sometimes in larger groups.

Distribution. North, Central and South America, Europe, Western Asia, Africa (north and south), introduced to Australia; in Europe very common and widespread, in Poland fairly frequent. Not legally protected in Poland.

Fruiting. From May to October; according to some descriptions mainly in autumn.

What can it be confused with?

• Agaricus arvensis (horse mushroom) and Agaricus campestris (field mushroom) — Can be told apart by smell (aniseed-almond instead of carbolic); they turn yellow much more weakly, not chrome-yellow and not immediately at the base of the stem.
• Agaricus bisporus (cultivated mushroom) — Sometimes confused; detailed differences: no data.
• Agaricus sylvicola (wood mushroom) and Agaricus sylvaticus (blushing wood mushroom) — Also similar; smell and taste distinguish the yellow-stainer from other agarics.
• Agaricus praeclaresquamosus, A. moelleri, A. pilatianus — Related species of the Xanthodermati group, also yellowing and smelling of phenol; A. praeclaresquamosus has dark grey scales, A. pilatianus has no bulbous stem.

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 name "carbolic" comes from the smell resembling carbolic acid (phenol), which strongly intensifies during cooking.
• About 50% of poisonings among collectors of agarics are caused by this species.
• In Italy it is expressly excluded from sale.