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Yellow Stainer (Agaricus xanthodermus)

Yellow stainer mushroom Agaricus xanthodermus showing white cap, pale gills, and yellow staining at the base of the stem Yellow stainer mushroom Agaricus xanthodermus cut open showing pinkish gills and bright yellow staining at the stem base Yellow stainer mushroom Agaricus xanthodermus growing in grass with white cap and yellow staining near the base of the stem

The Yellow Stainer (Agaricus xanthodermus) is one of the most commonly eaten poisonous mushrooms in the UK due to its resemblance to edible Agaricus species such as field and horse mushrooms. It grows in gardens, parks, woodland edges, and grassland from summer to autumn. The cap is white and smooth, and the gills turn from pink to brown as it matures, which often fools foragers.

When bruised or cut, the base of the stem and edges of the cap stain bright chrome yellow, especially when cooked. It also gives off a strong chemical or ink-like smell,often described as iodine or disinfectant. Eating this mushroom causes severe gastrointestinal upset, including vomiting, diarrhoea, and stomach cramps.

Identification Features:

  • Cap is white, smooth and rounded when young
  • Cap may develop slight brownish patches with age
  • Gills start pale pink, turning dark chocolate brown
  • Stem is white with a ring
  • Base of stem shows bright chrome-yellow staining when cut or bruised
  • Yellow staining is strongest at the stem base
  • Strong phenol / antiseptic / ink-like smell
    • Often described as hospital disinfectant
  • Flesh turns yellow quickly when damaged
  • Spore print is dark brown
  • Grows in grassland, parks, gardens and woodland edges
  • Often found in troops or small groups
  • Fruits summer through autumn in the UK
  • Frequently found in the same habitats as edible field mushrooms

Foraging Safety:

  • Poisonous - do not eat
  • Causes significant gastrointestinal distress
    • Nausea
    • Vomiting
    • Diarrhoea
    • Abdominal cramps
  • Not usually fatal, but can cause severe illness
  • Commonly mistaken for:
  • Key safety checks:
    • Cut the base of the stem - look for bright yellow staining
    • Smell carefully - strong chemical/phenol odour
  • Edible Agaricus species smell:
    • Pleasant
    • Mushroomy
    • Sometimes slightly almond-like
  • Yellow Stainer smell is sharp and unpleasant
  • Cooking does NOT make it safe
  • Often appears in lawns and parks, increasing risk
  • Children and pets may accidentally pick them
  • When foraging Agaricus species:
    • Always smell the base of the stem
  • If eaten accidentally:
    • Always check for yellow staining
    • Seek medical advice if symptoms develop
  • Best advice:
    • When in doubt, leave all white lawn mushrooms alone

Identification video:

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