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Paxillus involutus

[ Basidiomycetes > Boletales > Paxillaceae > Paxillus . . . ]

by Michael Kuo

Paxillus involutus is a widely distributed, variable species found under a variety of trees. Its gills are its most distinctive feature: they stain brown when damaged, and they are separable as a layer (push with a fingertip just above the apex of the stem). In northern and montane areas of North America, Paxillus involutus should be compared with Paxillus vernalis, which is nearly identical but features a somewhat wider stem (2-4 cm) and grows under quaking aspen and paper birch.

The Paxillus involutus group has been subjected to both mating studies (Fries, 1985) and DNA analysis (Jarosch & Bresinski, 1999), along with traditional morphological analyses--and results have upheld the idea that Paxillus involutus and Paxillus vernalis are biologically and genetically distinct, though they are difficult to separate on the basis of physical features.


Ecology: Mycorrhizal with a wide variety of hardwoods and conifers; apparently also capable of existing as a saprobe on wood; found in woods and in urban settings; growing alone, scattered, or gregariously; summer and fall; widely distributed in North America.

Cap: 4-15 cm; convex to broadly convex with a strongly inrolled, cottony margin; becoming planoconvex or centrally depressed; sticky or dry; smooth or finely hairy; brown to yellow-brown, olive brown, or grayish brown.

Gills: Separable as a layer; running down the stem; close or crowded; often becoming convoluted or pore-like near the stem; yellowish to pale cinnamon or pale olive; bruising brown to reddish brown.

Stem: 2-8 cm long; up to 2 cm thick; often tapered to base; dry; smooth or finely hairy; colored like the cap or paler; bruising brownish to reddish brown.

Flesh: Thick and firm; yellowish; discoloring brown when exposed.

Odor and Taste: Taste acidic or not distinctive; odor not distinctive or somewhat fragrant.

Chemical Reactions: KOH on cap surface gray.

Spore Print: Purplish brown to yellow-brown.

Microscopic Features: Spores 6.5-10 x 5-7 µ; smooth; elliptical. Pleuro- and cheilocystidia more or less fusoid; 40-90 µ long; with brown contents. Pileipellis a cutis of elements 3-6 µ wide,with brownish contents. Clamp connections present.

REFERENCES: (Batsch, 1786) Fries, 1838. (Fries, 1821; Saccardo, 1887; Kauffman, 1918; Smith, Smith & Weber, 1979; Fries, 1985; Thiers, 1985; Arora, 1986; Breitenbach & Kränzlin, 1991; Phillips, 1991/2005; Lincoff, 1992; Barron, 1999; Jarosch & Bresinski, 1999; Roody, 2003; McNeil, 2006; Miller & Miller, 2006.) Herb. Kuo 09120701, 09130703, 10031202.

Further Online Information:

Paxillus involutus at MykoWeb
Paxillus involutus at Roger's Mushrooms


Paxillus involutus

Paxillus involutus

Paxillus involutus

Paxillus involutus

Paxillus involutus

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Cite this page as:

Kuo, M. (2008, February). Paxillus involutus. Retrieved from the MushroomExpert.Com Web site: