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Boletus auriporus

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

by Michael Kuo

The identifying features of this beautiful mushroom include its bright yellow pore surface; its sticky stem, and its pinkish brown cap. In collections of mature mushrooms, the pore surface usually discolors pinkish or reddish on bruising. When young, the stem is typically adorned with tiny yellow granules or fibers. The cap surface does not flash green with ammonia, helping to separate it from the similar Boletus innixus, which demonstrates a green flash. It also lacks the yellow material on the stem, is completely dry under normal conditions, and has a pore surface that does not bruise or discolor. Additionally, it tends to grow in clusters, with the stem bases fused (and consequently pointed); Boletus auriporus, while not antisocial, has a more North American sense of "personal space."

Boletus viridiflavus was originally described by Coker & Beers (1943) from North Carolina. They described the cap color as "a peculiar olivaceous gold with reddish areas." In other respects the species is a dead ringer for Boletus auriporus. Coker & Beers used the name "Boletus auriporus" for the mushroom most authors now treat as Boletus innixus--so the question of whether or not Boletus viridiflavus is merely their name for Boletus auriporus arises. Singer (1947) and Both (1998) believed this was the case. Snell & Dick (1970) described the colors of "Pulveroboletus auriporus" to account for olive tones. Weber & Smith (1985) illustrate what I am calling Boletus auriporus as "Boletus viridiflavus." I have made several collections that appear to match the cap colors described by Coker & Beers for Boletus viridiflavus. While other features (including microscopic features and chemical reactions) are identical, the olive cap looks strikingly different in the field from typical Boletus auriporus specimens.


Ecology: Mycorrhizal with hardwoods, especially oaks; growing alone, scattered, or gregariously; summer and fall; eastern North America to Texas, and ranging at least as far south as Costa Rica.

Cap: 2-8 cm; convex, becoming broadly convex or almost flat; sticky when fresh; finely hairy or velvety; pinkish brown, fading in age; margin with a tiny extending sterile portion.

Pore Surface: Bright yellow; frequently bruising pinkish to reddish, especially in maturity; 1-3 pores per mm; tubes to 15 mm deep.

Stem: 4-12 cm long; .5-1.5 cm thick; more or less equal; sticky when fresh; yellow above, pinkish brown and streaked-looking below; with tiny yellow fibers when young and fresh; basal mycelium white; without reticulation.

Flesh: White or pale yellow; not staining on exposure.

Odor and Taste: The flesh tastes mild; the sticky to slimy material on the cap and stem is acidic (like putting your tongue on a radio battery). Odor not distinctive.

Chemical Reactions: Ammonia negative on cap and flesh; KOH negative to yellowish on cap and flesh; iron salts negative to yellowish on cap and flesh, dark green to blue on pore surface.

Spore Print: Olive brown.

Microscopic Features: Spores 11-16 x 4-6 µ; smooth; subfusoid; with dark brown (in a Melzer's mount) cystidia measuring 38-100 x 9-16 µ.

REFERENCES: Peck, 1872. (Saccardo, 1888; Coker & Beers, 1943; Singer, 1947; Snell & Dick, 1970; Smith & Thiers, 1971; Smith, Smith & Weber, 1981; Phillips, 1991/2005; Both, 1993; Both, 1998; Bessette, Roody & Bessette, 2000; Roody, 2003; Binion et al., 2008.) Herb. Kuo 07130401, 08200601, 07110701, 10170907.

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


Boletus auriporus

Boletus auriporus

Boletus auriporus

Boletus viridiflavus

Boletus viridiflavus?
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Kuo, M. (2004, July). Boletus auriporus. Retrieved from the MushroomExpert.Com Web site: