Yellow Stainer (Agaricus xanthodermus)

A cluster of Yellow Stainers.
A cluster of Yellow Stainers.

Phylum: Basidiomycota. Class: Agaricomycetes. Order: Agaricales. Family: Agaricaceae

Yellow Stainers are a very important mushroom to learn to identify because they are very similar to other local species of Agaricus mushrooms. The others are edible and delicious , Yellow Stainers are mildly toxic and taste of chemicals. They can be found in the same grassy areas as the edible species and are sometimes mixed in with them.

The general description of most Agaricus mushrooms apply to Yellow Stainers – a broad white/brown cap, a thick stem that is easy to separate cleanly from the cap and has a ring that is easily broken or removed, cuticle that can be easily peeled, crowded gills that darken with age, They also share a brownish spore print. Luckily though, there are differences.

The distinguishing characteristics of A. xanthodermus mushrooms are as follows –

  • Young specimens are flatter and almost box-like when compared to similar species
  • The stem is hollow on mature specimens
  • All parts of the mushroom will stain YELLOW when damaged.
  • The base of the stem often has a yellow tinge
  • Yellowing will turn brown after time
  • Gills are have a start as off white, become pinkish and then grey-brown
  • Cap does not have an in-rolled margin
  • The mushroom has a chemical smell, some say like ink. This smell intensifies with cooking,

As with all things, there is some variation between individuals. The yellowing can range from pale yellow through to a bright, chrome yellow. It always turns brown after a while. If in doubt, check the base of the stem, damage there will always turn yellow. The nase may even have a yellow tint when undamaged.

There are some folks who can eat Yellow Stainers without ill effects. Don’t risk it though! Poisoning will give you one to three days of diarrhea, vomiting, fever, chills, shakes, nausea, headache or any combination of those. You will generally feel lousy – I know I did! Don’t risk it, if it is yellowish and has a chemical odour, give it a miss.

Young ones are squarer and flatter than similar species.
Young ones are squarer and flatter than similar species.
The cuticle peels easily
Mature Yellow Stainer stems are hollow.
Mature Yellow Stainer stems are hollow.
The annulus is easily broken or removed.
The ring is easily broken or removed and the gills start whitish and develop a greyish tinge as they mature.

You can find the other local, edible Agaricus species on our Agaricus page and more delicious, local mushrooms covered on our Wild Fungi page.