Mycoscout How to identify the yellow stainer
The yellow stainer looks like a cultivated button mushroom that has escaped into a lawn: white cap, pink-then-brown gills, a ring on the stem. What gives it away is the reaction to damage. Scratch the cap or cut the stem base and the flesh turns chrome yellow within moments, fading to brown later, and the cut releases a smell of ink, phenol or iodine. Royal Botanic Gardens Victoria notes that in urban areas it is "much more common than edible mushrooms", and the Victorian Department of Health says it causes most poisonings from wild fungi in that state.
| Feature | Yellow stainer |
|---|---|
| Cap | 5–15 cm (First Nature); 50–200 mm (RBG Victoria); 6–15 cm (MushroomExpert). White, matt, often flat-topped and "a little squarer in profile" when young, greying or browning in the center with age. Bruises chrome yellow, especially near the margin, then browns. |
| Gills | Free, crowded. Off-white when the veil breaks, then pink, then grey-brown to dark purplish brown. Identical in color to the field mushroom's. |
| Stem & base | 50–150 mm long, 10–20 mm thick (RBG Victoria), smooth and silky, with a bulbous base. A large white pendulous ring that persists. The flesh at the stem base turns bright chrome yellow when cut, even in old specimens. |
| Flesh | White, turning chrome yellow when cut, most strongly at the base. |
| Spore print | Very dark brown to dark purplish brown. |
| Smell | Ink, phenol, iodine or "disinfectant", strongest when the stem base is cut or crushed and stronger again on cooking. Some people barely notice it; MushroomExpert's author describes himself as "smell blind" to it. |
| Habitat | Lawns, garden beds, parks, hedgerows, disturbed soil; in small groups, clusters or arcs. Mostly urban. |
| Season | June–October in Britain and Ireland; late summer and autumn after heavy rain in Victoria, sometimes year-round; summer and fall, or over winter in warm climates, in North America. |
| Range (US / UK & Europe) | US: probably widespread; documented from California and Illinois (MushroomExpert). UK & Europe: widespread. Also common in Victoria, Australia, where it causes most wild-fungus poisonings. |
Confirm these features
- Cut the stem lengthwise through the base: the flesh there turns chrome yellow at once.
- Scratch the cap edge with a fingernail: it bruises bright yellow, then goes brownish.
- Smell the cut base: ink, phenol, iodine or disinfectant, not aniseed and not "mushroomy".
- Gills off-white, pink, then grey-brown or purplish brown; spore print very dark brown.
- A large, persistent white ring and a bulbous stem base, but no sac or cup.
- Growing in grass, garden beds or along hedges, usually in a group.
Why one feature is never enough: the horse mushroom also yellows, just more slowly and less brightly, and some people cannot smell phenol. A white mushroom in grass with pure white gills and a sac at the base is not a yellow stainer at all but a deadly Amanita. Check the base, the stain, the smell and the gills together.
Dangerous look-alikes
The look-alikes here run both ways: the yellow stainer is picked by mistake for two edible species, and the white Amanitas can be picked by mistake for any of the three.
Field mushroom / meadow mushroom (Agaricus campestris)
Tell apart: the field mushroom never turns yellow when cut or bruised; its flesh stays white or goes faintly pink, and it smells like a shop mushroom. Its ring is thin and soon gone, while the yellow stainer's is large and lasts. Both have pink-to-brown gills, so gill color does not separate them. Risk: the field mushroom is edible; the danger is picking a yellow stainer with it. See field mushroom vs yellow stainer and the field mushroom page.
Horse mushroom (Agaricus arvensis)
Tell apart: usually larger (8–20 cm), with a double "cogwheel" ring and a strong aniseed smell. It yellows slowly and only slightly when bruised, and the stem base does not change quickly when cut. The yellow stainer's base goes chrome yellow immediately and smells of ink. Risk: the horse mushroom is edible; First Nature warns that the two are "very similar in appearance".
Destroying angel (Amanita bisporigera, A. virosa) and death cap (A. phalloides)
Tell apart: white gills at every age, a white spore print, and a sac-like volva at the stem base, often below the soil. The yellow stainer and the edible Agaricus species all have gills that turn pink and brown and a dark print. Risk: deadly, with no symptoms for 6–24 hours. See the destroying angel page.
Where and when it grows
The yellow stainer is a decomposer of rich, disturbed soil. First Nature places it under hedgerows and at the edges of parks and gardens; RBG Victoria lists lawns, garden beds among leaf litter and, in bushland, disturbed sites only. MushroomExpert gives grassy, cultivated areas and occasionally thin woods on the US West Coast. It fruits June to October in Britain and Ireland and in summer and fall in North America, over winter in warm climates. In Victoria it appears after heavy rain in late summer and autumn and can occur at any time of year.
Because it favors exactly the places people pick "field mushrooms", lawns, parks, verges and garden beds, it is the species most often eaten by mistake in Victoria, and First Nature calls it the one that "can cause serious stomach upsets". If it is coming up in your lawn, the mushrooms in lawn guide covers what else grows there.
Symptoms and why the delay matters
RBG Victoria attributes the toxicity to phenol. Symptoms are gastrointestinal: stomach cramps, nausea, vomiting, sweating and diarrhea (First Nature), or nausea, stomach cramps, diarrhea and vomiting "shortly after eating" (RBG Victoria), with severity depending on the amount eaten. This fits the gastrointestinal irritant pattern NAMA describes, with onset within 20 minutes to 4 hours. First Nature adds that a small minority of people eat it with no obvious effect, which explains why some foragers wrongly believe it is harmless.
The delay is the reason to act early rather than wait. NAMA's rule is that stomach symptoms starting 6–24 hours after a mushroom meal point to amatoxins, the deadly group, and the white Amanitas grow in the same lawns. If anyone has eaten a white lawn mushroom and you are not certain which, get help now and keep a sample of the mushroom. Do not wait to see whether symptoms arrive.
Using an app to check a find
A photo shows a white cap and, at best, pink or brown gills, which is the same picture an edible field mushroom gives. The yellow stain at the stem base and the phenol smell are things you have to do with a knife and your nose. Mycoscout leads with the verdict, shows its confidence, names the field and horse mushrooms as look-alikes and lists the stem-base test in its checklist, so you know what to cut before you decide. It is a field companion, not a clearance to eat; confirm any Agaricus with a local expert before it goes anywhere near a kitchen. More on what the app does at the Mycoscout homepage.
Frequently asked questions
What happens if you eat a yellow stainer?
Stomach cramps, nausea, vomiting, sweating and diarrhea, usually shortly after the meal. Severity depends on how much was eaten. Some people report no reaction, which is not a reason to eat it. Call poison control or emergency services now; do not wait for symptoms.
How do you tell a yellow stainer from a field mushroom?
Cut the stem base. The yellow stainer turns chrome yellow immediately and smells of ink, phenol or iodine. The field mushroom stays white or goes faintly pink and smells like a shop mushroom. The gills are the same color in both, so they do not help.
Yellow stainer vs horse mushroom: which yellows more?
Both can yellow, which is the trap. The horse mushroom bruises slowly and only slightly yellow and smells of aniseed; the yellow stainer goes bright chrome yellow at once, strongest at the stem base, and smells of ink or phenol.
Does cooking make a yellow stainer safe?
No. The Victorian Department of Health says there is no home test that separates safe from poisonous mushrooms, and First Nature notes the phenol smell gets stronger when it is cooked. Do not eat it.
Why is it called the yellow stainer?
Because the cap, stem and especially the flesh at the stem base turn bright chrome yellow when scratched, bruised or cut, then slowly fade to brown.
Sources
How we checked this page: the Mycoscout team cross-checked every edibility, toxicity and look-alike statement against the sources below on October 31, 2026. It has not been reviewed by a mycologist.
- Agaricus xanthodermus, Yellow Stainer, First Nature. Accessed October 31, 2026.
- Yellow-staining Mushroom, Agaricus xanthodermus, Royal Botanic Gardens Victoria. Accessed October 31, 2026.
- Poisonous mushrooms growing in Victoria (health advisory, 20 April 2026), Victorian Department of Health. Accessed October 31, 2026.
- Agaricus xanthodermus, MushroomExpert.com (Michael Kuo). Accessed October 31, 2026.
- Agaricus arvensis, Horse Mushroom, First Nature. Accessed October 31, 2026.
- Agaricus campestris, Field Mushroom, First Nature. Accessed October 31, 2026.
- Mushroom poisoning syndromes, North American Mycological Association. Accessed October 31, 2026.
