Observation 45991: Agaricus L.

When: 2010-05-28

Collection location: Silver Spring, Montgomery Co., Maryland, USA [Click for map]

Who: John S. Harper (jsharper)

Specimen available


Cap – 15.5 cm diameter, convex, creamy white, slight yellowing with abrasion, some brown/tan areas small scales (see photo close up)

Stipe – 10 cm x 3.5 cm, Swelling in the center, tapering above and below (spindle shaped not bulbous at base). Geyish pink above veil, creamy while like cap below, slight yellowing with abrasion. Does not turn bright yellow when cut.

Gills – free, pink, and in some areas greyish in sectors (see photo). Seems to be changing from grey to pink.

Veil and annulus – when first collected, slightly detached at edge of cap, later coming free and collapsing.

Odor – almond, especially at base of stipe when cut and crushed

Location – in grass/vegetation in an elevated median strip in a suburban area.

Additional note: At this same location, in October 2009 I found two specimens of similar stature and appearance. Separate observation to be posted. But for comparison, one picture posted here as well.

I have considered the following possible species, in order starting with most likely.

A. arvensis — aspects in favor. http://www.mushroomexpert.com/agaricus_arvensis.html. Size, almond odor, slight yellowing on abrasion of stipe and cap. Reasons for doubt: reported at as having gills “whitish at first, becoming brown (without a pink stage)”. However, different description of gills at http://www.mushroom-collecting.com/mushroomhorse.html as “grayish cream in immature unopened specimens. Shortly after the veil breaks pinkish at first, changing to brown and almost black at maturity.” [This really does seem to describe the gray portions shown in my photos, which seems to be the less mature areas. I definitely see pink here.] . Also reported to be “bulbous” at base. [That is not the case here.] Veil/ring characteristic of “cog wheel” did not appear to be present in this case. The time of year is wrong – should be late summer/fall.

A. macrosporus – [http://www.mushroomexpert.com/agaricus_arvensis.html. http://www.rogersmushrooms.com/....] Similar to arvensis discussion above: Additional factors in favor: cap “whitish splitting into large ochraceous scales or patches and the margin becoming toothed with age [not on this specimen because it was young, but this was true of one of the two specimens collected at this location in October 2009.] Stipe fusiform (spindle shaped). Almond odor reported to be faint. [Here I think pretty distinct.] Factors causing doubt: Gills whitish-grey at first, finally dark brown [notable pink in this specimen]; season described as “summer to autumn”. [It has been cool and rainy here recently, but with a brief warm spell near 90 degrees two days ago.] Habitat said to be pastureland; grows in rings [this was a solitary specimen].

A. bitorquis (syn. rodmani) – http://www.rogersmushrooms.com/.... Factors in favor: Right season – late spring to autumn. But otherwise, these descriptors seem to eliminate it: Cap 4–10cm across [instant specimen larger than this], convex soon flattened, white with faintly ochraceous flakes. [No sign of this]’ Stem white with two separate sheathing rings, the lower thinner and resembling a volva [Not positive, but did not seem to be two rings]; Flesh white, tinged faintly pink on cutting. [No pink] Smell pleasant [not just pleasant mushroomy in this case, but almond]; gills dirty pink at first, soon clay finally dark chocolate brown [I think it is going from grey/clay to pink]. See also description at http://en.wikipedia.org/wiki/Agaricus_bitorquis: equal to enlarged at the base, . . . thick white mycelial sheathing near the base". [here spindle shaped].

A. bernardii – [http://www.rogersmushrooms.com/.... and http://www.mykoweb.com/CAF/species/Agaricus_bernardii.html] Factors in favor: Description of cap "whitish and fairly smooth when young, becoming cracked or subscaly and often developing brownish colors [see picture of October specimen from same location]; Descriptions of gills vary: “pink becoming brown and then dark chocolate”. “pale grey then flesh-coloured” and “pinkish-tan becoming chocolate brown, finally blackish brown”. Eliminating factors: Reported to bruise and stain “reddish”. Smell reported variously as “fishy”, “brine or iodine”. “Habitat on sand dunes and meadows near the sea — but noted also on roadsides inland, possibly due to the practice of salting the roads in icy weather.” Season may be wrong for East coast — “autumn”, but in California reported as occurring in spring also.

A. xanthodermus –
http://www.mushroomexpert.com/agaricus_xanthodermus.html. Eliminating factors:
stipe “more or less equal; sometimes enlarged at the base”; bright yellow in the base of the stem when exposed to air"; “Odor unpleasant and phenolic”. “summer and fall”.

A. campestris – really, could not be – much too large to be, almond odor too distinct. Only thing in favor is the pink gills.

Species Lists


Foreground shows veil; background shows habitat (median of suburban street; some trees, grassy)
Attached portion of the veil when collected
Showing habitat – grassy, weedy. Size comparison to pocket knife
Note pink color of gills, with several sectors having a a grey color, and somewhat compressed (not fully expanded?) appearance.
Cut stipe at base did not turn strongly yellow
Close up of veil when collected
Close up of grey compressed area of gills
Close up of cap to show small scales
For comparision, similar speciment collected at this site in October 2009 – one specimen had a cracked cap, the other was smooth. See other observation for more details

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Created: 2010-05-28 17:21:12 -03 (-0300)
Last modified: 2010-05-28 17:39:47 -03 (-0300)
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