Agaricus campestris

This is a key to gilled mushrooms, that is, mushrooms having a definite cap with a fertile surface consisting of gills. The fruiting body usually also has a stem, although that may be lateral or absent (usually, then, the mushroom is growing from wood). You can use this key to identify mushrooms that you find.

Fruiting body containing fibers (usually in the stalk)

Gills free
Spore print chocolate brown
Annulus almost always present, usually membranous
The gills are usually pink or silvery-grey at first, but are colored chocolate brown at maturity from the developing spores
The cap and stalk are usually some sort of white or greyish brown, but may have fibrils or scales that are darker (like the portobello)
Growing on the ground, wood chips, or other organic debris

Partial veil thin, cottony
Annulus scant, sometimes absent
Flesh not changing color, either when bruised or in KOH
Gills commonly pink at first, changing to the color of the spores at maturity

Agaricus campestris     Linnaeus: Fries

Here are the characters that distinguish this species from the others in its group. For its more general characters, see higher up on the page.
If there's just a few words or a microscopic feature here, a more thorough description can be found above.

Diagnosis

• Cap up to 4" across; sometimes slightly fibrillose; usually white, sometimes greying or becoming brownish grey with age
  
• Usually in open, grassy areas

Microscropic Characters

• Spores 6-9 x 4-6 µm

Comments

I've never actually seen the greyer version illustrated here. Usually it's a dead ringer for the "button" mushroom in the store. There are several species that fit this description and must be distinguished microscopically - - although the flavor is supposed to be good, I've several times had collections that were completely and totally tasteless


 

 

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