I’m excited to have found my first Amanita on the property, but frustrated with my own inexperience with this genus. It’s made it a challenge to narrow down a more specific identification of this fungus in time for Mushroom Monday. However, it’s been a reminder that sometimes things are not always as they first seem, at least not in the world of fungi.
This fungus appeared after last week’s brief rain, growing under oaks and madrone on the western facing slope above the house. I saw it from at least 20 feet away, as its bright yellow cap stood out clearly among the brown leaves on the ground.
That it is an Amanita, I have little doubt. If the cap was red, I’d probably say its identification would be a slam dunk as the classic fly agaric, Amanita muscaria.
I’m presuming, based on some of the physical characteristics, that this is a yellow form of Amanita muscaria species, which are known to occur, but as to subspecies or variety, I can’t say conclusively. It’s possible it is Amanita muscaria var. formosa, but that variety is reportedly more common in eastern North America, than the west .
This specimen has some of the classic hallmarks of this group of agaric mushrooms, including a brightly colored cap, with warts, an annulus or skirt on the upper part of the stem, which was remarkably still intact, and scaly concentric shaggy ‘rings’ at the base of the swollen stipe.
Typical ofAmanita muscaria, this young specimen shows warts that are clearly yellow when young, but becoming white when exposed to sun. In the picture below, the more white colored warts were exposed to daylight, but the yellow warts toward the rear of the cap were still mostly under dirt and forest duff when I found this mushroom.
An interesting characteristic of these warts is that they were remarkably fragile, and sloughed easily, a trait perhaps more common to Amanita gemmata according to some sources [2,3], but there seems to be some contention as to whether A. gemmata truly occurs here. Just to add to my confusion.
The fragile skirt, or annulus, on the stem was clearly still intact, and is the first mushroom I’ve found on the property with an intact annulus. The edge of the annulus was distinctly flecked yellow, similar to the warts on the cap.
Pulling away the dirt toward the base of the stem it was clear the stipe was yellowish in color, and below the annulus, distinct bands of remnant veil material toward the base of the stem were apparent.
Unlike some Amanita species, there was no distinct cup-shaped volva at the base of the stem.
Unfortunately this was the only specimen found on the entire hillside, and on my return the next day to re-photograph it, something had clearly come along, dug it up, and absconded with it. A skunk perhaps, who recently always seems to be one step ahead of me on the mushroom hunting front! Some Russula sp., and numerous Hygrocybes that I’ve been watching develop this winter, have similarly disappeared with nothing but holes and claw marks in the soil where they once were. Clearly this creature is not a fan of ‘Mushroom Mondays’.
Another yellow species that has been identified in California is Amanita aprica. This toxic yellow Amanita species tends toward a more frosted appearance over the yellow cap, with rather more flattened and adherent warts, than distinct fragile, and pointed ones. The overall cap color of A. aprica is similar to this specimen, but generally it seems the stem is more stout and robust than this fungus appeared to be. It would have been helpful if I’d found more than one, in various stages of maturity. However, after a lot of reading, and poring through mushroom keys and photographs, it’s clear that the next specimen I find needs to be examined more closely, likely even at the level of a microscope, for a definitive ID. So for now, our best educated guess is a yellow variant of Amanita muscaria.
Note that we only hunt mushrooms with camera lenses here, but this genus deserves a significant amount of cautious respect from all mushroom hunters. Although some species of Amanita are edible, some of our deadliest mushrooms in this region also belong to this genus. Admittedly this yellow Amanita has little resemblance to our deadly Amanita phalloides (the Death Cap), or Amanita ocreata (the Destroying Angel), but it is very similar in color and form to Amanita aprica which is known to be toxic .
As such, we leave our foraging for kitchen-bound mushrooms to the experts, and we strongly suggest you do too!
 Mushroomexpert.com Amanita muscari var. formosa
 Mushroomexpert.com Amanita gemmata
 McKnight, K.H and KcKnight V.B. 1987. Peterson’s Field Guides – Mushrooms. p. 225
 Tulloss, R.E. and Lindgren, J. E. 2005., Amanita aprica—a new toxic species from western North America. Mycotaxon 91: 192-205.