Yellow Stainer

Where it grows

The yellow stainer fruits from summer through autumn in lawns, parks, woodland edges, and hedgerows on fertile soil. It is one of the most commonly mistaken Agaricus species and accounts for many of the mild mushroom poisonings reported each year.

How to recognise it

A white Agaricus that looks at first glance like a horse or field mushroom. Two reliable warning signs: when cut, the flesh at the very base of the stem turns an instant brilliant chrome yellow (the rest may yellow more slowly); and the smell, especially when the flesh is warmed in the hand or cooked, is a sharp chemical iodine-carbolic — sometimes described as old-fashioned hospital antiseptic or ink.

Edibility & cautions

Toxic to a large proportion of people: ingestion causes nausea, cramping, vomiting, and diarrhoea, usually within an hour or two. A small minority can eat it without reaction, which has muddied folk advice for centuries. Confusion with the field mushroom (Agaricus campestris) and the horse mushroom (Agaricus arvensis) is common. The chrome-yellow stem base and the carbolic smell are the dependable warnings — neither edible white agaric shares them. When in doubt, do a deep cut into the stem base and warm a piece in the hand before deciding.