Agaricus bisporus

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

Not staining red or yellow (even with KOH)
Scent mushroomy
Often browning where bruised or with age
Annulus persistent and membranous, but only one layer

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 6" across; covered with tufts of dark brown fibrils

Microscropic Characters

• Spores 5.5-8.5 x 4-6.5 µm
  
• Basidia mostly 2-spored

Comments

The stunted albino variety of this mushroom, var. hortensis, is the store-bought "button mushroom". The larger version described here, var. brunnescens, is sold under the trade names portobello, crimini, and more soon to be coming your way; but it also grows wild. It's not particularly common in our colder clime, though


 

 

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