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Strobilomyces confusus

[ Basidiomycota > Boletales > Boletaceae > Strobilomyces . . . ]

by Michael Kuo

Similar to Strobilomyces floccopus and often misidentified as that species, Strobilomyces confusus features smaller, more erect scales on its cap. The scales feel firm and semi-prickly, as opposed to the soft, woolly scales on Strobilomyces floccopus. I think the difference is especially notable when specimens are dried. However, the definitive way to separate the two species is to examine the morphology of the spores: Strobilomyces floccopus has conspicuously reticulate spores, while the spores of Strobilomyces confusus have spines and ridges but are not reticulate.

Since the ranges of the two species overlap in great part, and since there is a considerable "gray area" when it comes to assessing whether scales are small and erect or large and woolly, predicting which species one has collected has become one of boletology's favorite little challenges. Rolf Singer, who named Strobilomyces confusus in 1945, bragged that "[o]nce the distinguishing features are understood, they are so pronounced that it is possible to foretell what type of spores a certain dried specimen will have, and vice versa." Later, Walter Snell and Esther Dick (1970) raised the bar a little bit: "After a little experience, one can make a good guess between these two species." More recently, Ernst Both (1993) remarked: "It so happens that whatever we called S. confusus in the field turned out to be that in the laboratory. On the other hand, roughly half of the collections we called S. floccopus in the field turned out to be S. confusus under the microscope."


Ecology: Mycorrhizal with oaks; common; summer and fall; widely distributed east of the Rocky Mountains. The illustrated and described collections are from Illinois.

Cap: 3-10 cm; convex, becoming broadly convex; dry; covered with small, erect, fibrillose, black scales over a whitish to grayish ground color; the scales 1-3 mm wide at the base; the margin hung with remnants of a whitish to grayish partial veil.

Pore Surface: Whitish, becoming gray; bruising reddish gray, then dark brown to black; pores circular to angular, 1-3 per mm; tubes to 2 cm deep.

Stem: 4-10 cm long; 0.5-2 cm thick; more or less equal; whitish to grayish and reticulate near the apex; dark gray to black and shaggy below; at first covered with a sheathing, grayish partial veil, but soon with merely an ephemeral ring or ring zone; solid; base covered with dense, gray mycelium.

Flesh: Whitish throughout, turning reddish when sliced, then slowly red to dark red and eventually nearly black.

Odor and Taste: Not distinctive.

Chemical Reactions: Ammonia negative to slightly bluish on cap; negative to yellowish on flesh. KOH dark red on cap; orangish on flesh. Iron salts negative to bluish on cap; dark bluish on flesh.

Spore Print: Black.

Microscopic Features: Spores 9-12 x 7-12 µ (including ornamentation); globose to subglobose; with ornamentation of spines and occasional short ridges; not reticulate; brown in KOH. Pleurocystidia clavate to fusoid-ventricose; to about 60 x 25 µ; with brown contents in KOH. Pileipellis a trichoderm with cylindric to clavate terminal elements.

REFERENCES: Singer, 1945. (Singer, 1945; Snell & Dick, 1970; Smith & Thiers, 1971; Grund & Harrison, 1976; Smith, Smith & Weber, 1981; Weber & Smith, 1985; Halling, 1989; Phillips, 1991/2005; Metzler & Metzler, 1992; Both, 1993; Bessette, Roody & Bessette, 2000; Ortiz-Santana et al., 2007; Binion et al., 2008.) Herb. Kuo 07011301, 06291405.

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Strobilomyces confusus

Strobilomyces confusus

Strobilomyces confusus
Ammonia, KOH, iron salts

Strobilomyces confusus

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Kuo, M. (2015, January). Strobilomyces confusus. Retrieved from the MushroomExpert.Com Web site: confusus.html