Until the mid 1990s, this poisonous southern grassland species was not known to exist in Illinois. Today, it’s as common as grass--at least, in southern Illinois. During warm, muggy days of summer and sometimes into autumn, this distinctive Amanita pops up on lawns everywhere. What sets it apart from other white grassland mushrooms? The soft, powdery “cotton” covering the cap and stem instantly identifies this unusual Amanita when fresh. Unfortunately, rain often washes the mushroom clean, making instant identification trickier. An alternate, if less precise, method of Amanita thiersii identification: Lay a fresh cap, gills down, on a dark piece of paper for several hours to create a spore print. All species of Amanita (plus a few other genera of grassland mushrooms) produce white, dusty spore prints. Not brown. Not olive-green.  
White spores.