# Yellow stainer (Agaricus xanthodermus)

**Agaricus xanthodermus**

**Known today as.** A white field mushroom that bruises chrome yellow at the base and smells of ink or carbolic.

Kind: Fungus  
Poisoning: Gastrointestinal irritants (https://thethinkingpress.org/materia-medica/poisons/gastrointestinal)  
Toxic: yes

> **Caution.** Poisonous.

## What was it used for?

None.

## What does modern science say?

Causes vomiting and cramps in many who eat it, though some people seem unaffected.

## Pharmacognosy and toxicology

- **phenol**: the carbolic smell
- **4,4'-dihydroxyazobenzene**: the yellow

**Mechanism.** Phenol and related compounds irritate the gut; the mushroom is the commonest cause of mushroom poisoning in Britain, since it grows beside the edible field mushrooms it resembles.

**Dose.** A meal; some people eat it without harm.

**Standing.** None.

## What lore surrounds it?

The field mushroom’s treacherous double.

## Sources

- Phillips, R. (2006). *Mushrooms*.
- Gill, M., and Strauch, R. J. (1984). “Constituents of *Agaricus xanthodermus*: the first naturally endogenous azo compound.” *Zeitschrift für Naturforschung C* 39.

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*Yellow stainer.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-09-25. The Thinking Press. https://thethinkingpress.org/materia-medica/yellow-stainer

Historical description, not medical advice.