Cap 1.5-2.5 cm broad, egg-shaped in button-stage, becoming convex, eventually plano-convex; surface dry, the disc with lilac-brown to pinkish-brown fibrils, appressed fibrillose-squamulose towards the margin, the ornamentation over a pallid ground color; cuticle yellowing slightly where bruised or injured, yellow with KOH; context up to 3.0 mm thick at the disc, soft, thinning toward the margin; odor of anise; taste mild.
Gills free, close, cream-buff, blackish-brown at maturity; lamellulae up to three-seried.
Stipe 3.0-6.0 cm long, 2.5-3.5 mm thick, more or less equal, sometimes with a small basal bulb, hollow to stuffed at maturity; surface of apex, white, appressed fibrillose-striate, lower stipe sparsely covered with white squamules, yellowing slowly where handled; veil membranous, thin, white, leaving an inconspicuous, narrow, evanescent band high on the stipe or fragments on the expanding cap.
Spores 4.0-5.0 x 3.0-4.0 µm, broadly ellipsoid, smooth, thick-walled in face-view, inequilateral in profile, hilar appendage apparent, germ pore not conspicuous; spore print chocolate-brown.
Solitary or in small groups in mixed hardwood-conifer woods; fruiting early in the mushroom season; uncommon.
Probably edible, but too small and infrequent to be of culinary value.
This petite, woodland Agaricus has a stature and cap suggestive of a Lepiota. Its affinities, however, become obvious when the free, dark-brown (not white) gills, are seen. According to Alexander Smith, Agaricus diminutivus is part of a species complex with several forms occurring in the Pacific Northwest. The above description covers material seen along the Mendocino coast north of San Francisco. Agaricus semotus is similar, also occurs under trees, but is more robust, has a cap with a darker disc, and tends to have a clavate stipe.