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Pluteus americanus

[ Basidiomycota > Agaricales > Pluteaceae > Pluteus . . . ]

by Michael Kuo

Pluteus americanus is one of only a few species of Pluteus that stains blue, on the stem and the gills, when fresh. In North America the species has traditionally gone under the name Pluteus salicinus--but the latter species, recent research indicates, is strictly European (see Justo and collaborators, 2014). Pluteus americanus appears on the deadwood of hardwoods east of the Rocky Mountains--and, oddly enough, in eastern Russia.

Crucial microscopic features for Pluteus americanus, which should be checked if your goal is to eliminate all known look-alikes, include the pileipellis (a cutis), the pleurocystidia (with well-developed apical prongs), and the cheilocystidia (which are clavate). Matching these details will eliminate Pluteus cyanopus and Plutues phaeocyanopus (both with a cellular pilepellis), and the poorly-known Pluteus saupei (pleurocystidia with poorly developed prongs, cheilocystidia lageniform).


Ecology: Saprobic; growing gregariously on decaying logs of hardwoods; summer and fall; probably widely distributed east of the Rocky Mountains in North America; also recorded from eastern Russia. The illustrated and described collection is from Illinois.

Cap: 4-7 cm; broadly convex at first, expanding to planoconvex or flat; moist when fresh; very finely scaly over the center, but bald elsewhere; dark grayish brown when young and fresh, fading markedly as it dries out and eventually becoming very pale grayish brown or gray, with a darker center; the margin becoming finely lined for 10-15 mm.

Gills: Free from the stem or nearly so; close; short-gills frequent; white at first, becoming pink and, eventually, brownish pink; bruising grayish blue.

Stem: 4-6 cm long; 3-5 mm thick; equal above a slightly swollen base; bald or finely hairy; dry; whitish, becoming brownish with age; bruising slowly grayish blue; basal mycelium white.

Flesh: Very thin; white; unchanging when sliced.

Odor and Taste: Not distinctive.

Chemical Reactions: KOH negative on cap surface.

Spore Print: Brownish pink.

Microscopic Features: Spores 7-8 x 5-6 µ; broadly ellipsoid; smooth; hyaline with granular contents in KOH; inamyloid. Pleurocystidia 60-100 x 12-15 µ; subcylindric to widely lageniform, with apices crowned by 4-6 well-developed projections; walls 1-2 µ thick; hyaline in KOH. Cheilocystidia clavate; thin-walled; hyaline in KOH; abundant. Pileipellis a cutis; elements 4-10 µ wide, hyaline to faintly brown in KOH, smooth, septate, clamped at septa; terminal cells cylindric with rounded to subacute apices.

REFERENCES: (P. Banerjee & Sundberg, 1993) Justo, E. F. Malysheva & Minnis, 2014. (Kauffman, 1918; Singer, 1956; Banerjee & Sundberg, 1995; McNeil, 2006.) Herb. Kuo 07211502.

Further Online Information:

Pluteus salicinus var. americanus in Banerjee & Sundberg, 1993


Pluteus americanus

Pluteus americanus

Pluteus americanus

Pluteus americanus

Pluteus americanus
Spore print

Pluteus americanus

Pluteus americanus

Pluteus americanus

Pluteus americanus

Pluteus americanus
Clamp connection

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Kuo, M. (2016, June). Pluteus americanus. Retrieved from the MushroomExpert.Com Web site: