Agaricus species 01

[ Basidiomycetes > Agaricales > Agaricaceae > Agaricus . . . ]

by Michael Kuo

I find this little Agaricus in grassy edgewoods and disturbed ground in oak-hickory woods in central Illinois, in July and August. It has a pale yellowish brown cap that is covered with tiny fibers and scales, a (proportionally) tall and slender stem that features a thin white ring, and flesh that does not change color when sliced. Its odor is not distinctive. The cap surface turns yellow when a drop of KOH is applied.

It is reminiscent of a miniature Agaricus subrufescens, but its small size and lack of a strong almondy odor distinguish it. The species does not have a name--yet. But it has recently also been collected in Pennsylvania and in France (Kerrigan and Guinberteau, pers. com.), and a name is forthcoming.

Description:

Ecology: Presumably saprobic; growing alone or gregariously in grassy areas at the edges of oak-hickory forests--or along paths, in disturbed-ground or grassy settings within woods; July, August, and September; Coles County, Illinois.

Cap: 3-8 cm; blocky at first, before the veil ruptures; becoming broadly convex to planoconvex; dry; whitish to pale brownish underneath golden brown to brown, pressed-down fibers that separate with maturity and become aggregated into small scales over the disc; not bruising on the margin when rubbed repeatedly.

Gills: Free from the stem; close or crowded; short-gills frequent; white when young, going through a pink stage before eventually becoming dark chocolate brown; covered when in the button stage with a whitish partial veil.

Stem: 5-7 cm long; 6-10 mm thick; more or less equal; with or without a slight basal bulb; dry; smooth or finely hairy; with a fragile, skirtlike, whitish ring that occasionally disappears; whitish; not bruising or bruising faintly brownish on handling.

Flesh: White; not changing when sliced.

Odor and Taste: Not distinctive.

Chemical Reactions: Cap surface negative to weakly yellow with KOH.

Spore Print: Dark chocolate brown.

Microscopic Features: Spores: 6-8 x 3.5-5 µ; elliptical; smooth. Cheilocystidia scattered and infrequent; up to 24 x 12 µ; clavate to subfusoid.

REFERENCES: Herb. Kuo 07250302, 08280401, 08200504, 09230501, 09280503.

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Kuo, M. (2007, October). Agaricus species 01. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/agaricus_sp 01.html