Observation 103949: Xerocomus tenax Nuhn & Halling

When: 2012-08-05

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

Who: I. G. Safonov (IGSafonov)

No specimen available

The mushrooms are from 3 separate collection scattered under old oaks. Note the variability in the color of the stipe and color/intesity/mesh size of reticulation. All mushroom had a tough stipe tips.


Taken immediately after sectioning
Taken ~7 min after sectioning — note the bluing right above the tubes
Staining with ammonia = left half; staining with 3% KOH = right half
The cap diameter of this specimen was 13 cm

Proposed Names

76% (2)
Recognized by sight: Coarse red-brown reticulation on a whitish stipe; “woody” stipe base
Used references: “North American Boletes” by Bessette-Roody-Bessette
Based on chemical features: NH4OH on cap = gree-blue, resolving brownish; KOH on cap = deep red-brown
-28% (1)
Recognized by sight: According to Michael Kuo, B. illudens could be morphologically inseparable from B. tennax
Used references: MushroomExpert.com
85% (1)
Eye3 Eyes3
Recognized by sight

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Eye3 = Observer’s choice
Eyes3 = Current consensus


Add Comment
Really interesting…
By: Dave W (Dave W)
2017-10-29 12:54:18 PDT (-0700)

how these dissimilar examples of the same species were found growing in the same area. Puts to rest considering a suggestion that different forms may be regionally correlated.

By: I. G. Safonov (IGSafonov)
2017-10-28 21:14:15 PDT (-0700)

The featured fruitbodies were growing a few yards from each other in a grassy/mossy meadow. Note the variability in the degree and extensiveness of the reticulation. The caps are bleached out by the sun, so the original color would be darker. These are medium-sized mushrooms. I have not seen this species at this site since then (5 years!). Looking forward to finding it again, hopefully next year.

With regard to the two taxa in the summary line, the discussion in Smith & Thiers’ The Boletes of Michigan (TBoM) holds the key to understanding the modern conundrum. If you don’t have the physical book in hand, it’s available online at https://quod.lib.umich.edu/.... Illudens is on pp. 242-244 and tenax is on pp. 249-251.
The two gents never thought the two species were look-alikes of each other, as such a comparison is not featured in their book. Indeed, the photographs in the book (Plates 100 and 102-103, respectively) show the two species are very different mushrooms. How they became a species complex is a mystery.
Peck’s illudens type from 1896 is likely too old for sequencing. Hence, the MI illudens material of half the age can then be designated as the phylogenetic epitype (fingers crossed); the tenax type is of comparable age (50-55 y.o.), so it would be nice to get is sequenced ASAP, too.

Yeah, that specimen in the thumbnail photo is real nice.
By: Dave W (Dave W)
2017-10-28 18:14:55 PDT (-0700)

Actually, the mushrooms seen here are all Igor’s finds.

Thanks for bringing this back to my attention, Jason. I just now checked the newest NA bolete book, and indeed BRB have combined the species tenax/illudens under one name… just not clear which one they favor.

X. tenax
By: Jason Bolin (j.bolin@outlook.com)
2017-10-28 10:17:43 PDT (-0700)

Very nice find Dave. Beautiful specimen.

Provacative pairing …
By: Dave W (Dave W)
2012-08-06 06:41:26 PDT (-0700)

of one specimen that appears to be a bullseye ID for B. tenax, along with several other more ambiguous specimens. Chemical tests reported for B. tenax and B. illudens appear to be similar… depending upon how much difference one perceives between the colors brown and fuscous.

Created: 2012-08-05 15:29:18 PDT (-0700)
Last modified: 2017-10-29 12:57:22 PDT (-0700)
Viewed: 214 times, last viewed: 2017-11-01 08:41:30 PDT (-0700)
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