Notes: This is a very deceptive mushroom. It looks identicle to Agaricus campestris, the common (and edible) meadow mushroom. But, this one is NOT edible. To distinguish it from campestris, but a drop of KOH (Potassium Hydroxide) solution on the cap or stem. If it turns yellow, it is A. californicus. Another indicator is where it is growing. A. campestris growns in fields, as its name implies. A. californicus growns in woods. This sample was found under White Pine and near Oak in a mixed forest, not more than 10’ from a field. The KOH reaction is very rapid with a fresh sample, but may take a few minutes with an older mushroom. The photographs show mature specimens. The spore print is also identicle to A. campestris, a deep chocolate brown. What this mushroom is doing in Minnesota is a mystery to me as it is, by its name, a west-coast species. I have found this mushroom several times this year in many different locations, never in years past. It is a shame that it is somewhat poisonous as they are nice large mushrooms. The second photo shows the KOH reaction on the cap and stem.