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Agaricus placomyces

Page history last edited by PBworks 16 years, 3 months ago


Syn. Agaricus placomyces

(Basidiomycetes > Agaricales > Agaricaceae > Agaricus . . . ]

Taxonomy in Transition: ... > Agaricales > Lepiotoid Clade (J&V, 1998)


by Michael Kuo


This woodland species of Agaricus is found east of the Rocky Mountains, and appears to have a somewhat northern distribution. The flesh in the base of the stem is yellow, and the cap is covered with brownish fibers and scales, at least over the center. It is virtually identical to Agaricus praeclaresquamosus (see the right-hand column), a slightly larger species which grows in the west--and it is quite similar to Agaricus pocillator, a slightly smaller eastern species with a southerly range (see the comments below for help separating Agaricus placomyces from Agaricus pocillator).


According to most accounts, Agaricus placomyces develops brownish to yellowish droplets on the underside of its partial veil, which can be seen when the veil is still covering the gills. The droplets may be absent, however, or they may have dried out. In the latter case the result is frequently a discolored veil, the brownish droplets having created brownish stains. In the second and third illustrations to the right these stains can be seen; compare to the clean veil of Agaricus pocillator in the top illustration on the page for that species.


Agaricus placomyces is poisonous to some people; like most yellow staining species of Agaricus, it should be avoided.




Ecology: Saprobic; growing scattered or gregariously under hardwoods and in mixed woods; summer and fall; east of the Rocky Mountains, northern in distribution.


Cap: 5-12 cm, convex to broadly convex or nearly flat in age; dry; covered with brownish fibers and scales, especially over the center; whitish underneath, or pinkish in wet weather.


Gills: Free from the stem; crowded; pale grayish pink, eventually brown.


Stem: 6-15 cm long; 1-1.5 cm. thick; more or less equal, or with an enlarged base (but not typically ending in a small bulb like Agaricus pocillator); fairly smooth; white; bruising yellow, especially at the base; with a persistent ring; the partial veil when still covering the gills developing brownish to yellowish droplets.


Flesh: White throughout, staining bright yellow in the base.


Taste: Not distinctive or somewhat unpleasant; odor usually unpleasant (phenolic), but sometimes not distinctive.


Spore Print: Brown.


Chemical Reactions: Cap yellow with KOH.


Microscopic Features: Spores 5-7 x 3.5-5 µ; broadly elliptical; smooth.


REFERENCES: Peck. (Smith, Smith & Weber, 1979; Arora, 1986; Phillips, 1991/2005; Lincoff, 1992; Wood & Stevens, 2002.) Herb. Kuo 07200201, 07230303.


Agaricus meleagris is a former name--or perhaps a legitimate name for a similar species with a stronger phenolic odor, or perhaps a former name or synonym for Agaricus praeclaresquamosus. Some authors suggest that Agaricus placomyces, Agaricus praeclaresquamosus, Agaricus meleagris, and Agaricus pocillator represent a species cluster that has not yet been adequately explored and documented.


Several authors emphasize the width of the spores when separating Agaricus pocillator from Agaricus placomyces (the latter having broadly elliptical spores measuring 5-7 x 3.5-5 µ; the former with skinnier, elliptical spores measuring 4.5-6 x 3-4 µ). This seems unnecessarily arcane to me--and, more importantly, potentially inaccurate. In my collections, spore width ranges from 3-5 µ for both species, but important macrofeatures do not vary. Agaricus placomyces is somewhat larger than Agaricus pocillator, and has more brown scales and fibers away from the disc. Additionally, it lacks the small, abrupt bulb at the stem base and often (though not always) has brownish or yellowish droplets on the underside of the partial veil when it is still covering the gills.

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