Agaricus xanthodermus

Yellow Stainer Foraging & Identification Guide

The Yellow Stainer, or Yellow-Staining Mushroom, is a highly common, toxic wild fungus native to lawns, pastures, and garden beds across Europe, North America, and Australia. Growing in massive fairy rings in grassy suburban areas, it is a frequent cause of wild mushroom poisoning. While it looks virtually identical to the popular edible Field Mushroom and Meadow Mushroom, it possesses two flawless, golden diagnostic checks: its stem base turns a brilliant, instant chrome-yellow when bruised, and it emits a repulsive chemical smell of phenol or ink when heated.

Environment Grassy Lawns & Pastures

Humidity Moderate Humidity (50-60%)

Substrate / Host Rich Soil / Compost-rich Grass

Size 5cm - 15cm

Category Highly Toxic 💀

Botanical macro photography of Yellow Stainer (Agaricus xanthodermus) - Plant AI care database

How to Identify Yellow Stainer

A white mushroom resembling a field mushroom, but its stem base stains bright chrome-yellow instantly when bruised, smelling like ink when cooked.

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Cap: Varies by species.
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Spore: Critical check.

💡 Plant AI Tip: 💀 Phenol Toxicity: The Yellow Stainer contains high levels of phenol and related chemical irritants, which cause severe, rapid gastrointestinal cramps, vomiting, and diarrhea within 30 minutes of consumption.

Detailed Mycology Profile & Foraging Guide

Follow our detailed scientific field guide and environmental parameters to identify and study Yellow Stainer safely.

Grows on rich, composted soils in parks, green lawns, garden beds, and grassy pastures. It fruits in large groups, lines, or spectacular fairy rings from summer to late autumn.

Requires moderate moisture and warm-to-cool climates. It sprouts abundantly after heavy autumn lawn watering or rains.

Thrives in open, sun-exposed grassy lawns, though it can also grow in partial shade under garden shrubbery.

Cap is 5 to 15 cm, smooth white. Gills are initially pale pink, turning chocolate-brown as the spores mature, producing a chocolate-brown spore print.

Produces a dark chocolate-brown spore print. Highly identical to the spore prints of edible Agaricus species.

Flesh is white, staining yellow at the base. Stem is solid white, featuring a thick, double-edged white ring on the upper portion, lacking a volva.

Do not harvest. Gardeners and lawn owners should remove them to prevent pets or children from accidental ingestion. Always test the stem base of every wild Agaricus collected.

Highly toxic. It causes severe, sudden gastrointestinal poisoning with intense vomiting and stomach cramps. It smells so strongly of ink when heated that most people are deterred before tasting.

Rich in phenol and unique toxic compounds like agaritine derivatives. It has zero medicinal value and acts as a localized irritant.

CRITICAL WARNING: Dangerous edible look-alikes! The Yellow Stainer is the most common cause of mushroom poisoning because it closely resembles the choice edible Meadow Mushroom (Agaricus campestris) and Horse Mushroom (Agaricus arvensis). However, the edible species never stain chrome-yellow (Horse Mushroom stains slow pale-yellow and smells of sweet anise/almond), and they smell highly pleasant and sweet, whereas the toxic Yellow Stainer stains instant bright yellow at the stem base and smells strongly of phenol/chemical ink. Always scrape the stem base and smell wild white mushrooms!

The yellow staining reaction is most intense at the very bottom of the stem base. When identifying, always dig up the complete stem base, slice it vertically, and watch for the instant chrome-yellow color in the stem core.

Common Look-alikes & Foraging Danger

Fading Staining (Old Age)

Symptoms: Old, dry specimens do not turn yellow when the stem base is scraped.

Action: This is caused by dryness and age. The yellowing enzyme reaction slows down as the mushroom decays. Always smell old specimens; the chemical phenol odor remains active.

Cap Browning

Symptoms: The smooth white cap develops a dingy brownish-gray center, and the gills turn completely black-brown.

Action: This is natural spore maturation. The mushroom has completed its lifecycle. Discard and avoid contact with lawn compost.

Frequently Asked Questions

Why is it called 'Yellow Stainer'?

It is named 'Yellow Stainer' because its white flesh—especially at the very base of the stem—turns a bright, intense, chrome-yellow color instantly when scratched, cut, or bruised.

What does it smell like?

It has a distinct, unpleasant chemical smell resembling phenol, ink, iodine, or coal tar. This smell is sometimes faint when the mushroom is cold, but it becomes extremely strong and repulsive when heated.

How do you tell it apart from the edible Meadow Mushroom?

The edible Meadow Mushroom (Agaricus campestris) never stains yellow when bruised, lacks a chemical smell (smells pleasantly mushroomy), and has gills that start bright pink. The toxic Yellow Stainer stains instant chrome-yellow at the stem base and smells like chemical ink when cooked.

Is the Yellow Stainer lethal?

It is rarely fatal, but it causes very severe gastrointestinal illness. Consuming it leads to rapid, violent vomiting, stomach cramps, and diarrhea, starting within 30 minutes to 2 hours of eating.