Edible
Horse Mushroom
Agaricus fissuratus
The horse mushroom yellows slowly and mildly, not chrome yellow, its stem base does not turn yellow when cut, and it smells of anise or almond.
Yellow Stainer
Agaricus xanthodermus
Toxic lookalike
Also called yellow-staining mushroom, yellow-staining agaricus.
The yellow stainer is a white Agaricus that looks like a field or button mushroom but turns bright chrome yellow when bruised and smells of ink or phenol. It grows in lawns, gardens and parks and causes gastrointestinal upset in many people who eat it.
The tell
White Agaricus whose cap edge and stem base turn bright chrome yellow within seconds of being scratched or cut, with an ink or phenol smell.
Field marks
What to look at
Cap, underside and stem show in a photo. The spore print does not, and it is often the deciding check.
- Cap
- Rounded to squarish when young, then convex to flat. White to grayish, sometimes with a grayish brown center, smooth to finely scaly. Turns bright chrome yellow quickly when scratched, especially near the edge, then fades to brownish.
- Underside
- Gills free from the stem, crowded, whitish to pink at first, then chocolate brown.
- Stem
- White, with a thick, skirt-like ring. The base is often slightly bulbous, and the flesh inside it turns chrome yellow immediately when cut. No cup.
- Flesh
- White, turning bright yellow where cut, strongest at the stem base. Smell of ink, phenol or creosote, stronger when heated.
- Spore print
- Chocolate brown.
- Size
- Cap 2 to 6 inches wide (5 to 15 cm); stem 2 to 6 inches tall (5 to 15 cm).
Where and when
Where and when it grows
- Habitat
- Lawns, gardens, parks, hedgerows and the edges of woods, often in groups or rings.
- Grows on
- Soil and organic debris.
- Season
- Fall and winter in California; summer through fall elsewhere.
- Range
- Recorded mainly from California and the Pacific coast, with scattered records elsewhere; several similar yellow-staining species occur across North America.
Lookalikes
What the yellow stainer gets confused with
Each card says how to tell the two apart.
EdibleMeadow Mushroom
Agaricus campestris
The meadow mushroom is smaller, with bright pink young gills and a thin, fragile ring. It does not stain yellow and smells pleasant.
Agaricus bisporus
Photo coming
EdibleButton Mushroom
Agaricus bisporus
Wild button mushrooms bruise brownish to reddish rather than yellow and have a pleasant smell.
EdibleThe Prince
Agaricus augustus
The prince bruises yellow too, but its cap is covered in golden brown fibrous scales and it smells strongly of almonds.
Edibility
What the field guides say
Toxic lookalike
Field guides list the yellow stainer as poisonous. Recorded symptoms are gastrointestinal, including nausea, vomiting, diarrhea and cramps, usually within a few hours of the meal. Not everyone who eats it is affected. The cause is usually attributed to phenolic compounds, which also produce its ink-like smell.
This page states what field guides record. It is not advice to eat, taste or handle anything, and a photo cannot settle edibility. If someone has eaten a wild mushroom that may be toxic, call poison control (1-800-222-1222 in the US) right away, before symptoms start: the deadliest species act hours later.
FAQ
Questions about the yellow stainer
Is the yellow stainer poisonous?
Yes. Field guides list it as poisonous, causing nausea, vomiting, diarrhea and cramps within a few hours. Some people are not affected, which has led to mixed reports, but it is consistently listed as toxic.
How do you identify a yellow stainer?
Scratching the cap edge or cutting the base of the stem turns the flesh bright chrome yellow within seconds. It also has an unpleasant smell of ink, phenol or creosote. Edible lookalikes either do not yellow or yellow only slowly and mildly.
Where do yellow stainers grow?
In lawns, gardens, parks and along hedgerows, often in groups. In North America they are recorded mainly from California and the Pacific coast, where they fruit in fall and winter.
Sources
Where these facts come from
- Agaricus xanthodermus
MushroomExpert.com
- Agaricus xanthodermus
MykoWeb, California Fungi
- Agaricus xanthodermus
Index Fungorum
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