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Boletus innixus

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

by Michael Kuo

Boletus innixus is an attractive eastern bolete, recognized by its relatively dry, brown to reddish brown cap, its bright yellow pore surface, its bulbous stem with a small "root" below it, its tendency to grow in little clusters, and the absence of any bruising or staining reactions.

Boletus auriporus is similar, but has a quite slimy cap and stem when young and fresh. Its cap surface does not flash green with ammonia. In addition, its stem is not typically bulbous, it does not typically grow in clusters, its spores measure 11-16 x 4-6 µ, and it has white basal mycelium and tiny yellow granules or hairs on the stem. It is found under hardwoods east of the Rocky Mountains, and its range extends as far south as Costa Rica.

Boletus caespitosus and Pulveroboletus caespitosus are synonyms.


Ecology: Mycorrhizal with hardwoods, especially oaks; growing alone, gregariously, or (most typically) in small fused clusters; summer and fall; widely distributed east of the Rocky Mountains.

Cap: 3-8 cm; convex, becoming broadly convex; dry or somewhat tacky when wet; bald, but sometimes cracking in age; brown or reddish brown, fading to cinnamon tan.

Pore Surface: Bright yellow; not bruising; with 1-3 pores per mm when young, but pores up to 2 mm across in age; tubes to 1 cm deep.

Stem: 3-6 cm long; 1-1.5 cm thick at apex; usually bulbous, with a small rootlike projection below the bulb; dry, or often slimy near the base; more or less smooth; not reticulate; yellowish, with brownish streaks; basal mycelium yellow.

Flesh: White to yellow; often staining somewhat pinkish in the cap on exposure, or brownish in the stem.

Odor and Taste: Not distinctive.

Chemical Reactions: Ammonia flashing green, then resolving to dull orangish or reddish (with a greenish ring) on cap surface; pinkish to orangish on flesh. KOH dark red to reddish brown on cap surface; pinkish to orangish on flesh. Iron salts pale olive on cap surface; negative to grayish on flesh.

Spore Print: Olive brown.

Microscopic Features: Spores 8-11 x 3-5 µ; smooth; subfusiform.

REFERENCES: Frost, 1874. (Frost, 1874; Saccardo, 1891; Snell & Dick, 1970; Smith & Thiers, 1971; Grund & Harrison, 1976; Weber & Smith, 1985; Arora, 1986; Phillips, 1991; Both, 1993; Both, 1998; Bessette, Roody & Bessette, 2000; Roody, 2003; Binion et al., 2008.) Herb. Kuo 08050308, 09180301, 06290704, 08280902.

This site contains no information about the edibility or toxicity of mushrooms.


Boletus innixus

Boletus innixus

Boletus innixus

Boletus innixus

Boletus innixus

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Kuo, M. (2003, August). Boletus innixus. Retrieved from the MushroomExpert.Com Web site: