Identifying Agaricus xanthodermus (yellow stainer mushrooms)

“Are you going to write about mushrooms that look good or mushrooms that taste good? Or both?” asked my boyfriend.
“Errhhh…neither.” I responded. “They look boring and are usually poisonous.”



I recently ran into these mushrooms down the street from my house, and since they are so easy to mix-up with edible varieties, I figured I could help spread info on how to ID these fellas. If you have any more helpful info or experience with these mushrooms – I’d love to hear it! As a hobbyist, I hope to only contribute info that would help others as much as it has helped me, and put out helpful data to the universe.

Say hello to Agaricus xanthodermus, commonly called “yellow stainer,” and for a great reason!

Also in the family Agaricus are common button mushrooms (Agaricus bisporous) and field or meadow mushrooms (Agaricus campestris). These mushrooms are widely cultivated, and the kind you are most likely to buy in a grocery store. 

Most of the specimens I have pictures of are more mature, so they look a lot like what’s sold as portabella mushrooms.

I thought I had found either the button or the meadow mushroom branch of the family, but I found some helpful information that helped me ID that I, in fact, had the poisonous branch of the Agaricus family: Rub the mushroom. 

When Agaricus xanthodermus are rubbed on the stem or cap, they soon develop a yellow stain. After reading this info, I was confused by it and didn’t think the staining would be so obvious, but it absolutely is. This is a great tip for beginning mushroom hunters like me, and can easily be done in the field before you harvest too many mushrooms.


Agaricus xanthodermus. Yellow staining quite visible around edge of cap. 


(To make matters slightly more confusing, just because your mushrooms stains yellow doesn’t necessarily mean it will give you an upset stomach. Yellow stainers are sometimes not poisonous mushrooms. If you have yellow staining as well as a strong chemical smell coming from the mushroom, then it’s probably not a safe mushroom to eat. However, I don’t feel confident enough in my ID skills yet, so if I have an Agaricus mushroom staining yellow, I wouldn’t risk eating it.)

Here’s a video of me rubbing up on a mushroom. I was struggling to find good enough lighting to show the yellow stain, but I think this will be helpful:


Here are some great links if you’re interested in IDing these and other members of the Agaricus family: