Amanita muscaria var. guessowii
Amanita muscaria var. formosa pic 1.jpg
A mature Amanita muscaria var. guessowii mushroom under a northern white pine in Ovid, Michigan, United States
Scientific classification edit
Kingdom: Fungi
Division: Basidiomycota
Class: Agaricomycetes
Order: Agaricales
Family: Amanitaceae
Genus: Amanita
A. m. var. guessowii
Trinomial name
Amanita muscaria var. guessowii
Amanita muscaria var. guessowii
View the Mycomorphbox template that generates the following list
gills on hymenium
cap is flat or convex
hymenium is free
stipe has a ring and volva
spore print is white
ecology is mycorrhizal
edibility: poisonous or psychoactive

Amanita muscaria var. guessowii, commonly known as the American yellow fly agaric, is a basidiomycete fungus of the genus Amanita. It is one of several varieties of the Amanita muscaria fungi, all commonly known as fly agarics or fly amanitas.



The cap is 4.5–16 (18) cm wide, convex, and becomes broadly convex to flat in age. It is bright yellow or yellow-orange, usually more orange or reddish orange towards the disc, and fading to pale yellow. The volva is distributed over the cap as cream to pale tan warts; it is otherwise smooth and sticky when wet. The margin becomes slightly striate in age. The flesh is white and it does not stain when cut or injured.


The gills are free to narrowly adnate, subcrowded to crowded, cream to pale cream, truncate, unevenly distributed, of diverse lengths, and plentiful.


Amanita muscaria var. guessowii spores are white in deposit, broadly ellipsoid to ellipsoid (infrequently subglobose or elongate) and inamyloid. The spores are (7.0–) 8.7-12.2 (-14.8) x (5.9) 6.5–8.2 (9.5) µm.


The stipe is 1–3cm, more or less equal or narrowing upwards and slightly flaring at the apex. It is white to yellowish cream, densely stuffed with a pith, the skirt-like ring is membranous, persistent, the lower stipe and upper bulb are decorated with partial or complete concentric rings of volval material that are bright pale yellow to cream or sordid cream.

Microscopic features

Clamps are present at bases of the basidia.

Distribution and habitat

Amanita muscaria var. guessowii is found growing solitary or gregariously, it is mycorrhizal with conifers mostly but also deciduous trees as well, it is found often in the fall but sometimes in the spring, common in the northeast, from eastern Canada to North Carolina west to Michigan.[1]


Main article: Muscimol mushroom

As with other Amanita muscaria, the guessowii variety contains ibotenic acid, and muscimol, two psychoactive constituents which can cause effects such as hallucinations, synaesthesia, euphoria, dysphoria and retrograde amnesia. The effects of muscimol and ibotenic acid most closely resemble that of a Z drug, like Ambien at high doses, and not a classical psychedelic, i.e. psilocybin.

Ibotenic acid is mostly broken down into the body to muscimol, but what remains of the ibotenic acid is believed[according to whom?] to cause the majority of dysphoric effects of consuming A. muscaria mushrooms. Ibotenic acid is also a scientifically important neurotoxin used in lab research as a brain-lesioning agent in mice.[2][3]

As with other wild-growing mushrooms, the ratio of ibotenic acid to muscimol depends on countless external factors, including: season, age, and habitat - and percentages will naturally vary from mushroom-to-mushroom.


See also


  1. ^ "Shroomery - Hunting Fly Agarics in North America".
  2. ^ Becker, A; Grecksch, G; Bernstein, HG; Höllt, V; Bogerts, B (1999). "Social behaviour in rats lesioned with ibotenic acid in the hippocampus: quantitative and qualitative analysis". Psychopharmacology. 144 (4): 333–8. doi:10.1007/s002130051015. PMID 10435405. S2CID 25172395.
  3. ^ Isacson, O; Brundin, P; Kelly, PA; Gage, FH; Björklund, A (1984). "Functional neuronal replacement by grafted striatal neurones in the ibotenic acid-lesioned rat striatum". Nature. 311 (5985): 458–60. Bibcode:1984Natur.311..458I. doi:10.1038/311458a0. PMID 6482962. S2CID 4342937.