Observation 142676: Russula mutabilis Murrill

When: 2013-08-13

Collection location: Maple Shade, New Jersey, USA [Click for map]

Who: I. G. Safonov (IGSafonov)

No specimen available

I found these under oaks, but apparently they also grow in a linden tree plantation.

The caps are deep orange-brown at maturity (it rained recently, so maybe the moisture has darkened the colors), but paler when young, shaped like a cushion at buttons stage and flat and a bit depressed at full maturity. The cuticle peels about 1/2 in fresh samples, but an older and drier specimen peeled less than 1/3. The cap margin is striate-pulverulent. The largest cap is 8-9 cm across.

The stipes are stout, enlarging downward, whitish to pale yellow at the apex, darker yellow on the bottom half, with brown stains (prior to handing). They tend to hollow out at maturity or with connecting or non-connecting chambers when younger.

The odor of fruitbodies is strong and undiminishing; they smell like benzaldehyde, somewhat fruity, but with a fetid touch toward the end of inhalation, especially in older specimens.

The cap flesh/gills definitely taste acrid/hot, but the sensation is not immediate (10-15 sec) and gradually increases in intensity. However, they are nowhere as hot as Lactarius piperatus or Lactarius deceptivus.

Without a doubt these belong to the fetid Russula group. Macroscopically, they originally keyed out to foetentula/fragrantissima/granulata/laurocerasi (cap color “C” = yellow, ochre, orange). But then I noticed what appeared to be a yellowish powder on the cap margin of a button specimen and dropped KOH on cap and stipe, which readily produced an orange-red reaction. At the same time, I didn’t notice any surface reddening after handling.

Conclusion: I think these are closer to R. mutabilis. The spore shape & ornamentation (isolated warts with a few occasional joined connectors) seem to be in good agreement with this assignment, too, though the spore print en masse is in the “B-C” range rather than “C-D”.


Staining of the cap with KOH
Staining of the stipe base with KOH
1000x magnification, mounted in 5% Lugol’s

Proposed Names

46% (2)
Recognized by sight: Strong odor of benzaldehyde with a touch of fetidness
50% (3)
Used references: 1) Kirby/Fatto Russua guide
2) MushroomExpert.com
Based on microscopic features: Spore ornamentation
Based on chemical features: KOH staining cap and stipe orange-red

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Eye3 = Observer’s choice
Eyes3 = Current consensus


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Created: 2013-08-14 15:39:37 PDT (-0700)
Last modified: 2016-04-21 11:04:14 PDT (-0700)
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