Observation 29295: Agaricus L.

Habitat: under Douglas-fir, growing on composted Douglas-fir and Bigleaf maple leaves, mixed with some grass clippings.

[admin – Sat Aug 14 02:01:21 +0000 2010]: Changed location name from ‘I-5 Rest area N-bound near Wilsonville, Oregon’ to ‘I-5 Rest Area, near Wilsonville, Oregon, USA

Proposed Names

61% (2)
Eye3 Eyes3
Recognized by sight: The annulus should make this an easy one to key out.
37% (2)
Used references: Arora’s Mushrooms Demystified, p. 339; noted for robust size/cap with yellowish fibrils on an otherwise mostly white background, and an annulus which is nearly cogwheel-like.
29% (3)
Recognized by sight

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Eye3 = Observer’s choice
Eyes3 = Current consensus


Add Comment
By: Daniel B. Wheeler (Tuberale)
2011-04-10 09:33:51 PDT (-0700)

were you referring to A. smithii? If so, at least some Agaricus do seem rather specific in the substrate preferences. I agree saying Sitka spruce to be a specific preferred substrate might be going too far. There certainly was no Sitka spruce within at least 40 miles of this location.

It seems odd to me that no Agaricus expert has suggested alternatives to this. I only thought of it as a curiosity as it didn’t seem to match much in my usual book sources.

If we assume assume composted Douglas-fir and Acer macrophyllum leaves are the major components of the substrate as they appeared to be, the range of this species should be much wider than currently known.

Could it be that rare? Or just rarely collected?

I apparently did not add much of description to the photos. Here’s some addenda: with basal bulb; color of entire sporocarp yellowish, including flesh near the bottom of the stipe (see fingernail scratch on bottom photo); annulus nearly cogwheel-like. While the admin has changed the location somewhat, it should be noted there are 2 rest areas at this location, and this was found on the eastern-most off Interstate-5 heading north: less than 1/2 mile away from the other rest area, but I have not found the fungi at that location.

If this is growing on Douglas-fir/Bigleaf maple compost, it should be found at nearly ever Interstate-5 rest area in Oregon, as those trees are abundant and common in Western Oregon.

Agaricales of CA
By: Christian (Christian Schwarz)
2011-04-10 08:22:32 PDT (-0700)

notes caps starting “pallid”, becoming minutely “apressed-squamulose” (see lower photos), and habitat as “mixed conifers…from Mendocino to Oregon”.

Agaricus is saprobic as far as we know, so I think saying Sitka Spruce is the “host” makes it sound too specific.

Similar in color and stature to these:

By: Darvin DeShazer (darv)
2011-04-09 21:34:58 PDT (-0700)

Not a good fit for A. smithii. The cap is too pale and the fibrils are too short and they should be appressed. Sitka Spruce is the host for A. smithii.
In favor of A. smithii, the annulus and the basal bulb look good, as does the smooth stipe.

More slender, upright stature
By: Christian (Christian Schwarz)
2011-04-09 19:23:02 PDT (-0700)

and northern distribution suggest that it is not A. summensis

Created: 2009-11-30 17:04:14 PST (-0800)
Last modified: 2011-09-29 16:22:51 PDT (-0700)
Viewed: 126 times, last viewed: 2017-06-06 04:18:12 PDT (-0700)
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