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Boletus atkinsonii

[ Basidiomycetes > Boletales > Boletaceae > Boletus . . . ]

by Michael Kuo

This eastern member of the Boletus edulis species group is distinguished by its roughened and somewhat wrinkled cap surface (which becomes minutely patchy at maturity), its preference for hardwoods, and its characteristic reactions to chemicals--including a gorgeous purple reaction to ammonia.


Ecology: Mycorrhizal with hardwoods, especially oaks and beech; growing alone, scattered, or gregariously; summer and fall; widely distributed in eastern North America.

Cap: 4-20 cm; convex, becoming broadly convex or almost flat; dry; finely roughened; somewhat wrinkled; often becoming cracked in age; grayish brown to yellowish brown; margin even.

Pore Surface: White when young, becoming yellowish or brownish yellow; not bruising; pores "stuffed" when young; at maturity with 1-3 round pores per mm; tubes 5-12 mm deep.

Stem: 5-12 cm long; 1-3 cm thick; more or less equal, or enlarging to base; dry; solid; whitish or brownish; prominently reticulate with brownish reticulation.

Flesh: White; not staining on exposure.

Odor and Taste: Not distinctive.

Chemical Reactions: Ammonia flashing purple to magenta, then resolving to purplish or brownish on cap surface; negative on flesh. KOH brown to pale orange on cap surface--sometimes flashing purplish first; negative on flesh. Iron salts negative on cap surface and flesh.

Spore Print: Yellowish brown.

Microscopic Features: Spores 10-14 x 3.5-5 µ; smooth; subfusoid to fusoid.

REFERENCES: Peck, 1904. (Saccardo, 1912; Snell & Dick, 1970; Smith & Thiers, 1971; Both, 1993; Bessette, Roody & Bessette, 2000.) Herb. Kuo 07309701, 07220321, 09190302, 06300711, 07060702, 06230902.

Boletus nobilissimus, recently described from New York, appears to me to be nearly identical to Boletus atkinsonii.

Further Online Information:

Boletus atkinsonii in Smith & Thiers, 1971


Boletus atkinsonii

Boletus atkinsonii

Boletus atkinsonii

Boletus atkinsonii

Boletus atkinsonii

Boletus atkinsonii spores

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Kuo, M. (2010, March). Boletus atkinsonii. Retrieved from the MushroomExpert.Com Web site: