Macrolepiota mastoidea is a species of mushroom producing fungus in the family Agaricaceae.
It was first described by many mycologists throughout the 1800s and classified variously as Agaricus gracilentus, Agaricus mastoideus, Agaricus umbonatus with each synonym then undergoing its own extensive period of reclassification. It got its current name Macrolepiota mastoidea in 1951 when classified by the German mycologist Rolf Singer.
It grows up to wide and tall. The cap is white with brown scales in the center. The stem has a ring and is enlarged at the base.
It can appear similar to some toxic Chlorophyllum species.
This species is found in Europe from August to November.
The species is reported to be edible, sans the tough stem, but it can appear similar to some toxic species.