about 12cm in diamater
stalk stained bright yellow when cut

Proposed Names

86% (6)
Recognized by sight
Used references: Mushrooms Demystified by David Arora
-20% (4)
Recognized by sight: yellows at base; xanthodermus yellow quickly at cap edge.

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= Observer’s choice
= Current consensus


Add Comment
a sample size of one …
By: Debbie Viess (amanitarita)
2011-09-22 08:17:27 PDT (-0700)

does not always provide enough information to determine an ID. Agaricus species in general can be quite tricky. But the fact that your fruit body is showing yellow at the cap edge, along with habitat and other characteristics, is sufficient to make a determination of xanthodermus, your original ID.

More importantly, you now know not to eat this group, all of which smell of phenol and some of which yellow.

Indeed the base of your single specimen is more brightly yellow than is typical for californicus, but the crooked stipe is found with both species. Arora shows a photo of a crooked stipe californicus in MDM, ironically enough, since his descriptions have been quoted here.

The real trick is not so much WHICH toxic yellowing species of grass dwelling Agaricus that you have in hand, but how to tell the many delicious and edible Agaricus species from the toxic ones. And that will only come with time and experience.

Spore measurements are well beyond the abilities of most here; edibility determination, rather than species determination, does not require a microscope.

I don’t think the cap yellowing
By: Christian (Christian Schwarz)
2011-09-22 07:53:13 PDT (-0700)

is the main feature to pay attention to, but your photo does show yellow stains on the paper, which I would NOT expect from A. californicus.

Stature, and staining in the base are more important in my mind. Spore measurements would add another level of certainty, but in my mind, this already looks like a typical A. xanthodermus.

New Photo Upload
By: Janet Hsiao (jhsiao)
2011-09-21 22:49:21 PDT (-0700)

I have attached a picture that was taken earlier today while I took a peek at my spore print set up. There’s a faint yellow mark where the edge of the mushroom was, as shown. Is that a prominent enough stain to consider it a xanthodermus?

By: Christian (Christian Schwarz)
2011-09-21 17:48:13 PDT (-0700)

the infrequent/inconsistent staining sounds right for A. californicus.
I look forward to seeing some pictures and maybe spore measurements.

The relative commonality of each species is an issues I’ve been meaning to sort out for awhile. I’ll do a bunch of collections/measurements this seasons.

By: Byrain
2011-09-21 17:35:26 PDT (-0700)

I don’t have collections or good pictures of them, I was planning on doing more work on them when they start fruiting again here. The form I found doesn’t stain like a highlighter the way A. xanthomdermus does nor does it stain consistently, but when it does stain its mostly the base and can occasionally be a rather strong reaction.

From Mushrooms Demystified:
By: Christian (Christian Schwarz)
2011-09-21 17:03:27 PDT (-0700)

“Typical forms of A. californicus – (if they can be said to exist) – do not stain bright yellow like A. xanthodermus.”

Byrain – if your collections have been staining bright yellow, is there some opposing reason you have been calling them A. californicus? – spore size is a good alternative way to tell them apart. A. californicus has longer and broader spores.

From Kerrigan:

A. californicus – spores 5.4-6.0 × 4.1-4.6
cheilocystidia present

A. xanthodermus – spores 5.0-5.4 × 3.5-4.4
cheilocystidia present, abundant

By: Byrain
2011-09-21 16:40:21 PDT (-0700)

You can see where its begging to stain around cap margin in the first picture. In my experience, what I have been calling Agaricus californicus stains a lot in the base, less so elsewhere while A. xanthodermus does this:

still have the mushroom?
By: Debbie Viess (amanitarita)
2011-09-21 16:26:32 PDT (-0700)

rub the cap edge.

By: Christian (Christian Schwarz)
2011-09-21 16:09:44 PDT (-0700)

Stains bright yellow in the stipe base, as shown.

In my experience A. californicus has less of a bulbed, crooked base, and doesn’t stain anywhere near as brightly yellow, sometimes appearing to hardly stain at all.