Truffle Genus: Agaricus

Kingdom: Fungi Phylum: Basidiomycota Order: Agaricales Family: Agaricaceae

Spore Characters

Surface: Smooth.
Shape and Size: Subglobose to globose, 6-8 (-10) x 5-8 µm.
Wall: Thick.
Color in Water: Dark brown.
Melzer's Reaction: None.
Comments:  The smooth, subglobose, thick-walled, dark brown spores are diagnostic. The 3-layered spore wall of A. inaspertus is distinctive for truffle-like fungi in north temperate forests.

View photos of Agaricus spores

Sporocarp Characters

Shape and Size: Pulvinate, subglobose to globose-depressed.
Peridium: Unpolished, obscurely fibrillose.
Gleba: Sublamellate, somewhat powdery when mature, black.
Odor: Disagreeable.
Comments: Appears as a somewhat distorted, unopened Agaric.

View photos of Agaricus sporocarps

Name Derivation

Agaricus, from the Greek Agaricum, a type of tinder conk (perhaps also pertaining to the region "Agaria Sarmatica", now part of Ukraine and adjacent areas); inaspertus which means closed, used by Vellinga et al. (2003) to denote the enclosed sporocarps.

Distribution

Idaho, Oregon, and California in montane conifer forests.

Season: Late summer.
Species known from North Temperate Forests: One truffle-like member (Agaricus inaspertus) in an otherwise large genus of mushrooms.

Keys and Descriptions

Singer and Smith (1958) as Endoptychum depressum.

References
Singer, R. and Smith, A.H. 1958. Studies on secotiaceous fungi - II. Endoptychum depressum. Brittonia 10:216-220
Vellinga, E.C., de Kok, R.P.J., and Bruns, T.D. 2003. Phylogeny and taxonomy of Macrolepiota (Agarcaceae). Mycologia 95:442-456.