Notes:
Cap up to 6 cm is white and smooth at first with a yellow brown disc. Gills are white at first then pink then brown. Superior veil is fragile. Stem context is hollowing. Other characteristics can be seen in the photos. Mild odor. Gregarious under native mesquite at about 3400’.

Species Lists

External Links

Images

KOH on flesh of stem base and right side of cap. Analin on left of cap and more orange than photo shows.
A+A on left, KOH on right

Proposed Names

-57% (1)
Based on chemical features: KOH +; Aniline + Acetic acid (see comment below)
36% (2)
Recognized by sight: in the A. caribaeus complex
Used references: see phylogenetic tree

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= Observer’s choice
= Current consensus

Comments

Add Comment
Terri,
By: I. G. Safonov (IGSafonov)
2020-04-27 17:57:45 PDT (-0700)

The 3 caribaeus accessions are 100% identical with respect to each other. Your critter is 7 characters off, of which one is an ambiguity. Of the remaining ones, four are C-T mismatches, and perhaps one can make a feeble argument – in defense of potential conspecificity – that some of these could be written off as potential fully polymorphic sites (i.e., there could be caribaeus collections out there that have a “Y” at these positions). Still overall it feels like a bit of a stretch… What about the difference in cap surface pigmentation seen in https://www.flickriver.com/... and https://www.neotropicalfungi.com/...?

Yes, you are right this is A+A
By: Terri Clements/Donna Fulton (pinonbistro)
2018-09-30 06:59:46 PDT (-0700)

Just confirmed with Chris May who made it. It is half aniline and half glacial acetic acid.

Chemical question
By: Rick Kerrigan (rwkerrigan)
2018-09-30 06:32:31 PDT (-0700)

Is the analine in the presence of an acid? Strong acetic acid will do; I call this the A+A reaction/test. Analine alone doesn’t do much on Agaricus.

Minores species often give a good scarlet reaction, but orange is plausible for A+A.