Please do not re-click a link while waiting for a page to load. (It’s slower and degrades site speed for all users.)
To get images for machine learning, see MO Images for Machine Learning


This may be A. augustus, or it may be the Eastern North America entity Arora mentions that possesses smaller spores (I haven’t had a chance to look at Bessette, Bessette and Fischer yet). Average spore size is 7.14 × 4.41 um, which is a little on the small side for A. augustus.
I have not observed this locally before (in twelve years). Note the beautiful floccose stipe and underside of the annulus.
Specimen at MSC (accession number will be added when obtained).

[admin – Sat Aug 14 01:57:27 +0000 2010]: Changed location name from ‘East Lansing, MSU campus, Ingham Co., Michigan, USA’ to ‘Michigan State University, East Lansing, Michigan, USA’


Proposed Names

13% (7)
Recognized by sight
Used references: Arora, Mushrooms Demystified
18% (7)
Recognized by sight: Cap is wrong for A. augustus.
44% (8)
Recognized by sight
45% (2)
Recognized by sight
66% (2)
Used references: Dr. Richard Kerrigan (rwkerrigan)

Please login to propose your own names and vote on existing names.

= Observer’s choice
= Current consensus


Add Comment
Agaricus nanaugustus Kerrigan
By: Danny Curry (DCurry)
2016-11-03 02:29:32 CET (+0100)

Thank you, very much, Rick Kerrigan !
I’ve collected several specimens of this species from SW. Ohio and have been, woefully, unable to key it closer to anything other than A. augustus !
( much to everyone’s amazement )
It’s a relief to, finally, have this connection confirmed.
( and a proper taxon for it ! )

New name now available: Agaricus nanaugustus
By: Rick Kerrigan (rwkerrigan)
2016-11-03 01:31:54 CET (+0100)

On October 25 2016 the name Agaricus nanaugustus Kerrigan was published. I think it is likely, but not certain, that Heather’s collection belongs to this new species (although in my experience the cap has usually been more expanded and becomes more tawny than in her photos). A. nanaugustus and A. subrufescens have been confused for a very long time, although they don’t look all that similar to each other.

A. nanaugustus is phylogenetically very close to A. augustus. However, while visually similar, it is not as robust, and it has smaller spores. It is known so far from the Northeast and occasionally from the Southwest… and so far NOT from where A. augustus is reliably documented.


A species of interest
By: Rick Kerrigan (rwkerrigan)
2009-06-18 22:23:21 CEST (+0200)

Hello from Rick Kerrigan,

As my name showed up somewhere in this discussion, I decided to offer the following:

First, A. subrufescens Peck definitely, always has a glabrous stipe, period. Regrettably, some confusion arose from Kauffman’s (1918) reinterpretation of Peck’s original concept (Kauffman sometimes ‘corrected’ Peck about Peck’s own species!… in fact Peck is correct). Kauffman’s incorrect concept (having an ornamented stipe) has unfortunately but understandably been followed by some authors and web-posters in the midwest and northeastern USA.

Heather’s Michigan fungus, based on the photos, belongs to a different branch of the genus that includes from 2 to 4 species (the actual number remains to be determined). They include (1) A. augustus, well-known from western North America; (2) a similar unnamed species I’m in the process of describing from PA and IL, with smaller dimensions and smaller spores; (3) IF it is different, Kauffman’s species, with even smaller spores, and; (4) IF it is different, Heather’s collection, with spores like Kauffman’s. Items (3) and (4), both from Michigan, need careful study, and (2-4) presently remain conceptually entangled with one another and unfortunately also with the false concept of A. subrufescens. Heather’s (4) may ultimately be a match for my (2); however based on available info the color and spore size may not be precisely the same. Either way, at this time no correct, valid name has ever been published for Heather’s collection (or my own) — it will have to be described as a new species. Science marching on…

I’ve cultured and DNA-sequenced (1), (2), and A. subrufescens, and know them well. I hope to study (3) and (4) soon. For more information on A. subrufescens you can check out my 2005 Mycologia paper [97(1): 12-24], and the older literature cited therein.

If you can hold this clearer but still cloudy picture in your mind while it gets further sorted out, a better story should emerge before too long. I hope this has been helpful. Thanks to David A., who brought this post to my attention.

Cheers — Rick

good discussion
By: Debbie Viess (amanitarita)
2008-10-13 20:02:03 CEST (+0200)

and interesting to have these regional differences illuminated.

East vs West, cont.
By: Heather Hallen-Adams (hallenhe)
2008-10-13 15:51:39 CEST (+0200)

It does match the Bessette, Bessette and Fischer description and pictures nicely. Arora’s comments under subrufescens are “In eastern North America, an edible Agaricus with tawny scales on the cap (like A. augustus), a shaggy stalk, and weaker almond odor has also gone under the name A. subrufescens, apparently because of its similarly-sized spores. Whether it is a distinct species or merely an extreme form of A. subrufescens is for licensed Agaricus-experts to decide.”

East vs West material
By: Darvin DeShazer (darv)
2008-10-11 17:08:06 CEST (+0200)

Spore size does not match A. augustus, but it does fit A. subrufescens. Bessette, Bessette and Fischer as well as Smith and Weber have a photo that matches the cap AND the shaggy stipe. Dr. Rick Kerrigan says the stipe is “subglabrous above, covered below with short, erect, largely deciduous fibrils” and the “UV also leaving short, erect, deciduous fibrils on stipe from annulus to basal region”. However, his color photos (2) show a smooth stipe.

Like Nathan, I have grown this species from a kit and it had a smooth stipe. Both of Arora’s books show a smooth stipe, so maybe it is an East vs West characteristic. Smith’s guide to Western Mushrooms also shows a shaggy stipe, but he could have used a photo from a different location.

I think this was the original cultivated button mushroom a century ago and for some flavorless reason it was replaced with the button mushroom, A. bisporus. I also seem to recall that Kerrigan made it synonymous it with A. blazei and A. braziliensis, but I could not find the reference to reread the exact details. Maybe someone will know if it is true or not.

Arora, D. 1986. Mushrooms Demystified. Ten Speed Press, Berkeley, CA. 959p.
Arora, D. 1991. All That the Rain Promises, and More…A Hip Pocket Guide to Western Mushrooms. Ten Speed Press, Berkeley, CA. 259p.
Bessette, A., A. Bessette and D. Fischer 1997. Mushrooms of Northeastern North America. Syracuse University Press, Syracuse, NY. 582p.
Kerrigan, R. W. 1986. Agaricaceae. 62p. Thiers, H. D., editor. 1982-1997. The Agaricales (Gilled Fungi) of California. Mad River Press, Eureka, CA
Smith, A. H. 1975. A Field Guide to Western Mushrooms. Univ. of Michigan Press, Ann Arbor, Michigan. 280p.
Smith, A. H. and N. S. Weber. 1980. The Mushroom Hunter’s Field Guide: All Color and Enlarged. Univ. of Michigan Press, Ann Arbor, Michigan. 316p.

agaricus sp.
By: vesna maric (kalipso)
2008-10-11 13:46:08 CEST (+0200)

It looks like A. augustus to me too.

Not A. subrufescens
By: Nathan Wilson (nathan)
2008-10-11 04:32:50 CEST (+0200)

Doesn’t match my experience of A. subrufescens from collecting in southern California, Honduras or Brazil. I’ve also grown it in my backyard from a kit. A. augustus is closer, but I agree with Darvin. The cap doesn’t match my experience from western US for that taxon.

subrufescens not one I see out West…
By: Debbie Viess (amanitarita)
2008-10-11 01:12:42 CEST (+0200)

…but your specimen seems to have an awfully shaggy stipe for that species. not quite like an augustus, either. Am I seeing some reddening on the caps edge?

I am assuming that it had a strong almondy odor, or neither of these names would have been chosen!

I vote Agaricus sp., with out more info…