A pure white mushroom with chocolate brown spores, commonly known as the horse mushroom, A. arvensis has a delicious rich flavor that falls somewhere between portobellos and sweet almond. It is not as almondy as A. augustus, which makes it a bit easier to cook with. I found these specimens in late Autumn, and again in Springtime, in Palo Alto, CA, near some live oaks. Be very careful not to confuse this mushroom with Amanita ocreata, which can kill you. Check the base to make sure it has no volva (sac) and carefully note the brown gill color. More often, this mushroom can be confused with the yellow-staining A. californicus or xanthodermis, which smell acrid (phenolic), stain bright yellow around the edge of the cap and base, and often have gray shading in the cap. While the horse mushroom will stain slightly yellow, it has a sweet odor that separates it immediately from its emetic cousins, and the base of its stem does not stain yellow like the others.
Highly recommended and delicious. One of my favorites!