Horse mushroom

Description

The horse mushroom is a large, white or cream agaricus with a cap 7–20 cm across, which yellows when pressed. The young gills are pale, then grey-brown and chocolate, and the stem has a large, drooping, double ring. It smells of aniseed or almonds.

It grows from May to October in meadows, pastures, gardens and forests, also in rings, often on fertile soils, near stables. In Poland it is common.

The greatest risk is confusion with the white, deadly poisonous amanitas (the destroying angel, the fool's mushroom and the white form of the death cap). They are distinguished by the volva and bulb at the base of the stem and by gills that are white at any age. Agaricus mushrooms should be collected only by experienced mushroom pickers; if you are not sure, do not eat it.

Identification features

Cap

Diameter 7–20 cm; egg-shaped when young, then hemispherical, convex, mature flat. Surface bare, silky-shiny, dry, white to cream; yellows when pressed.

Hymenophore (underside of the cap)

Gills free, crowded; white when young and white for a long time (according to some descriptions pale pink to white), then grey-brown, finally chocolate-brown to blackish-brown; according to other descriptions they never have a pink tinge.

Stem

Height 5–15 cm, thickness 1–3 cm; cylindrical, thickened at the base, first solid, then tubular, breaks off easily from the cap; yellows when pressed. Large drooping ring, double, with "cogwheel" (toothed) patterns on the underside, whitish above, sometimes with yellowish scales beneath.

Flesh

Soft, elastic, white, sometimes yellowish in old specimens. Taste insignificant, smell of aniseed (according to some descriptions almond, marzipan, from benzaldehyde); the smell disappears after cooking. Do not taste the flesh of unidentified mushrooms.

Spore print and spores

Spore print blackish-brown to purple-brown (according to some descriptions dark brown). Spores smooth, brown, 6–8 × 4–5 µm.

Habitat and distribution

Ecology. Saprotroph. Grows on the ground in meadows, pastures, gardens, in coniferous, deciduous and mixed forests, in forest nurseries, on various organic waste; often near stables and among nettles (nitrogen-rich soils). Forms fairy rings. On the west coast of North America associated with cypresses, in the east with spruces.

Distribution. North and South America, Europe, Asia, Australia. In Poland common. Not legally protected; also described as common and not threatened.

Fruiting. From May to October (in Great Britain from July to November); singly or in small groups.

What can it be confused with?

• Amanita virosa (the destroying angel; Polish: muchomor jadowity), Amanita verna (the fool's mushroom; Polish: muchomor wiosenny), white form of Amanita phalloides (the death cap) — Deadly poisonous; gills always white (never darkening), white spore print, volva and bulbous base of the stem. Agaricus mushrooms have gills that turn brown with age and a dark spore print. In young specimens the gills are hidden under the veil.
• Agaricus xanthodermus (the yellow stainer; Polish: pieczarka karbolowa) — Poisonous (causes stomach disorders). Also yellows when pressed, but smells of carbolic acid (phenol).
• Agaricus silvicola (the wood mushroom; Polish: pieczarka bulwiasta) — Also smells of aniseed, but the gills stay red-pink for a long time.
• Agaricus campestris (the field mushroom; Polish: pieczarka łąkowa) — Similar, smaller; detailed differences — no data.
• Agaricus osecanus — Rare; does not have an almond smell.

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 epithet arvensis means "of the field"; the English name "horse mushroom" refers to its occurrence near stables.
• The almond (marzipan) smell comes from benzaldehyde.
• It is one of the largest white agaricus mushrooms in Great Britain.
• On the underside of the ring a "cogwheel" (toothed) pattern is visible, resulting from the double structure of the ring.