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White yellow stainer with a bright yellow cut stem base
Poisonousintermediate

Yellow Stainer

Agaricus xanthodermus

A white Agaricus that instantly stains chrome yellow when scratched, especially at the cut stem base, and smells of ink.

Photo: Anisha Kumra, CC BY
Compiled by Mushroom Forage Map field deskExpert review pendingContent checked
Toxicity warning

Poisonous. The most common cause of Agaricus poisoning. Always cut the stem base and smell the flesh.

Season
Summer to autumn
Habitat
Gardens, parks, hedgerows, and woodland edges
Underside
Free gills, pink then chocolate brown
Spore evidence
Dark brown

Where it grows

Tracked records and known growing zone

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Squares: where people recorded it, brighter where more people did
Verified records
4,720
People who recorded it
2,365
Most records (northern hemisphere)
Sep–Dec
Records span
1999–2026

Research-grade iNaturalist records, snapshot Aug 27, 2026. The growing zone combines areas where different people have repeatedly verified it. Records show where people looked and found it, not current abundance or permission to gather.

Observation season

When field records occur

Choose a hemisphere · All recorded years; not a current forecast.

Choose the hemisphere you want to study. Country detection is approximate and some countries span the equator.

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Lookalikes to rule out

Meadow mushroom does not stain yellow and smells pleasant.

Horse mushroom yellows slowly and smells of aniseed.

Identification

The cap is white, often squarish in outline when young. Scratch the cap edge or cut the base of the stem and it turns bright chrome yellow within seconds. The smell is of ink, phenol, or hospital disinfectant, strongest when cooked. Gills turn pink, then brown.

Why it matters

Yellow stainer causes vomiting and diarrhea. Some people tolerate it, which gives it an inconsistent reputation, but it is responsible for many Agaricus poisonings.

Memorable fact

The yellow fades to brown within minutes, so check a fresh cut.

Sources

Never eat a mushroom from this page alone

Confirm identity using the whole specimen, multiple reputable sources, and a qualified local expert. Identified edible species still require appropriate preparation. Cooking does not make a poisonous mushroom safe.

Safety and poison response
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