Amanita vaginata?

[CamilleR]

Found on the ground in oak woods.

[Dave W]

Lack of a partial veil (no ring), striate cap margin, and saclike membranous basal volva (universal veil) all point toward the group of species within genus Amanita section Vaginatae that many field guides call "Amanita vaginata". A. vaginata is actually not known to occur in NA. It's a Eurpoean species. Further complicating matters is that there are a variety of different NA species that more-or-less fit the description of A. vaginata. Some of these species have globose (round) spores, and others have ellipsoid spores. The NA pale/grayish/silvery-capped Vaginatae are still being sorted out. They're a challenging group. I have contributed a fair amount of material --along with descriptions and occasionally estimates of spore measurements-- to this cause. Actually, the entire section Vaginatae is an ongoing mycological project. Multiple new species have been been proposed these past 10 years or so. 

[CamilleR]

Thanks Dave. I didn't know there were so many different types of that mushroom.

[Dave W]

Here's a link to Rod Tulloss's Amanita Studies website. It's a list of all the named species in Amanita section Vaginatae (worldwide). Also, there's quite a few designated by numbers/letters, These come from collections that may or may not represent distinct --as yet unnamed-- species.  http://www.amanitaceae.org/?section+Vaginatae  NA field guides typically list two species, A. fulva and A. vaginata. The true A. vaginata isn't even known to occur in NA!