Fungus on my mind-- The Yellow Stainer

Agaricus xanthodermus is a common mushroom in California that one can often find in their backyard or on the side of the road. On campus these white lovelies can be found under the pine trees in the court yard nestled between Muir Biology building and Ledden Hall. Agricus is an important genus of mushroom; I am sure most people in America have eaten at least one—unless you were a very stubborn child—because the common supermarket mushroom comes from this genus. A. xanthodermus commonly known as Yellow Stainer is a poisonous variety of mushroom that if eaten will leave you next to a toilet all weekend. How does one identify an Agricus let alone a yellow stainer you ask?

First, turn the mushroom over. If it is an Agricus, the gills will be a rosy clay color when young, eventually turning into a brown color when older. Next disconnect the stem from the cap to see if the gills are free from the stem—if so, continue on.

To find the spore colors take the fresh cap of the mushroom and place it on a white piece of paper and let sit so that the spores can settle onto the paper. If the spores are a chocolate brown you are most likely in possession of an Agricus!

Agricus houses many species of both poisonous and edible qualities, yet each one has a special combination of features that give the key to its identity. For the yellow stainer, when the stalk is crushed it gives off an unpleasant smell of antiseptic (like phenol) and when the flesh of the mushroom is bruised it turns yellow. Yet the most defining feature is that when the tip of the stalk is cut it is a very bright yellow, much more so then any other part of the body of the mushroom and more so then any other Agricus.

The Yellow Stainer when cooked smells and tastes horrible and if eaten gives you gastrointestinal distress—overall not a very nice mushroom, yet fun to find. Happy hunting!