This sort of the documented species fly agaricis distinguished by its yellow to orange, instead of the red cap. Other trademark features are shared with the red version: numerous warts on the cap, a hoop on the upper stem, and a particular stem base that features several shaggy "zones" of velum material on the top fringe a basal bulb. Fly agaric var. guessowii is found within the northern Midwest and eastern North America from the northeast's boreal forests, south to the Appalachians.
In northern Michigan Amanita Muscaria var. guessowii fruits in high quantities, it usually is attaining dinner-plate size. Since it's a reasonably gregarious mushroom, one often finds large troops of those mammoth Amanitas lurking under European quaking aspen at the fields' sides.
Compare this mushroom carefully with fly agaric var. flavivolvata and fly agaric var. persicina, both of which have ranges that partially overlap the range of Amanita Muscaria var. guessowii. Also, compare with Amanita gemmata and Amanita russuloides, which may look superficially similar but feature very different stem bases.
The variability name Formosa designates Latvian variety and not consistently described in EU literature. This mushroom is usually featured in field guides as "Amanita muscaria var. Formosa," However, the varietal epithet guessowii represented a North American mushroom and was applied by Veselý (1933) to acknowledge the version of Fly Agaric described by Canadian Hans Güssow.
The taxonomy of the fly agaric species group will very likely change within the near future. A 2006 study by Geml and collaborators found DNA support for the thought that the color of the cap and warts in fly agaric isn't necessarily indicative of phylogenetic differences. The study used molecular dating techniques to hypothesize that "the ancestral population of Amanita muscaria likely evolved within the Siberian-Beringian region and underwent fragmentation . . . the info suggests that these populations later evolved into species, expanded [sic] their home in North America and Eurasia" (225). As for the typical morphological features separating "varieties," the researchers noted that among the species determined by DNA, "all . . . share a minimum of two morphological varieties with other species, suggesting ancestral polymorphism in pileus and wart color pre-dating their speciations."