Collection location: Howarth Park, Santa Rosa, California, USA [Click for map]
Found growing with bay, coast live oak, douglas fir. When I pulled away the duff to see the base of the stipe, I found that it was basically growing on a piece of decayed leaf and it fell over, still “stuck” to the leaf. The pileus was moist but not viscid and mauve, with yellow fibrils covering it. Both the stipe and the edge of the pileus yellowed (an ochre yellow) as I handled it. The pileus was 5 cm across and the stipe was 1 cm across at the apex and widened at the base. The stipe was creamy white with some clear yellow at the base, before I touched it, and then it was tinged ochre/yellow all over.
Few mushrooms are as strong as H. russocoriaceus :-). Agaricus is a bit more subtle and sometimes needs a bit of encouragement to get the odor to come out. I find that scratching the base of the stipe is best for the phenolic smelling ones, and scratching the edge of the cap is best for the almond ones.
For future reference, would I be able to catch the odor by getting up close and personal? Do I have to crush part of it? Would it be like the Camarophyllus russocoriaceus and be obvious even from afar?
Odor is a really important feature for telling apart the two groups of yellow staining Agaricus. There is one group that has a sweet/almond/anise scent and another that has an unpleasant chemical, phenolic scent. First group are all good edibles. The second are best avoids as they cause many people to throw up.
Based solely on the photos, I would guess that this is one of the sweet ones and most likely A. silvicola, but I’d have to look at it and smell it to be sure.