Agaricus
Note the reddish stains on the stem of this guy, just seconds after being pulled from his place under the log. In Colorado they have a similar mushroom they call "amicosa" and they avoid eating it. This material came from Papoose Creek, MT, and had a nice smell so I gave it a try.
It was quite alright. Generally, eating red or brown staining Agaricus from a woodland setting is not recommended. A. sylvaticus has now been split into several species, some are edible, some are not. Stay with the yellow-staining woodland agaric, A. silvicola and you will be fine.
Brazillian Agaricus
This is the first image taken of the mushroom. Note the faint pinkish stain where it was bruised in picking. It had rained the night before, and I found this early in the morning.
This shows the mushroom in its natural setting, in Iguazu park on the Argentine-Brazilian border. Note the annulus.
Two days after seeing this Agaricus at Iguazu, I returned to see the specimens looking just a bit more bruised, and the gills much darker from the maturing chocolate brown spores. You can easily see the free gills in this photo.
Agaricus silvicola is a pleasant scented, yellow staining mushroom that grows in the conifer forests and glens, waiting until after the solstice to fruit usually but not always in pairs. A. albolutescens stains and smells even more. Some variability exists in this group. Make sure you can distinguish these from Stropharia ambigua.
This image portrays and contrasts two species of Agaricus that grow in coastal Oregon east to the Kootenai NF. A. praeclarosquamosa, the lighter cap with grayish fibrils, isn't food and neither is A. subrutilescens, which always has that white stalk below the veil.
This is an image of a very common but inedible Agaricus which keys to hondensis in some books but I'm inclined now to call it californicus. It has had quite a naming history here, as species split and one hundred flowers bloom and a hundred schools of thought flourish. There are many more images of this variable mushroom somewhere.
As might be suspected, this is the classic A. hondensis from the coast. Note the multi-hued bruising and staining reaction on the stem, which changes visibly over time. The reddish brown fibrils in this pattern on the cap is characteristic as well.
Agaricus augustus is a welcome guest at any picnic. They call it the prince for a reason. I've only seen this a few times in Missoula yards. We also have A. rutilescens and some other mushrooms that may be here because they were imported by settlers in the last century.
