Cap 2.5-4.0 cm broad, at first convex-cylindrical, expanding to plano-convex; margin incurved, then decurved, in youth often fringed with veil fragments; surface dry, appressed fibrillose to sparsely squamulose towards the margin, the ornamentation pinkish-brown to lilac-brown over a pallid background, with age the fibrils brownish, the cap bruising yellowish slowly; context pallid, firm, up to 5.0 mm thick at the disc, unchanging or darkening only slightly when injured; odor and taste pleasant, of anise.
Gills free, close to crowded, relatively broad, up to 4.0 mm, at first cream-buff, then pinkish-tan, finally medium-brown; lamellulae in four to five series.
Stipe 2.5-4.5 cm long, 4.0-7.0 mm thick, equal or slightly enlarged at the base, fragile, stuffed at maturity; surface whitish with appressed fibrils above and below, occasionally fibrillose-striate near the apex, bruising yellowish to tawny; partial veil fibrillose-membranous, thin, white, the unbroken veil sometimes yellowish in areas, forming a thin, whitish to tan-colored, narrow, pendulous, superior annulus, soon disappearing or collapsing against the stipe.
Spores 4.5-5.0 (5.5) x 3.0-3.5 µm, elliptical in face-view, slightly inequilateral in side-view, smooth, thick-walled, many with a dark central body, hilar appendage inconspicuous; spore print dark-brown.
Solitary to scattered, sometimes in arcs in grass; fruiting in late summer in watered areas or soon after the fall rains; uncommon.
Edible, but too small and infrequent to be of culinary value.
This small grass inhabitant is recognized by a cap with pinkish to purplish fibrils concentrated at the disc. With age these become brownish and frequently tinged yellowish where handled. Closely related is Agaricus comptulus, another small, anise-odored species found in grass, but it has a cream-colored cap. Like Agaricus micromegathus, it yellows slowly where injured. Also similar are Agaricus semotus and A. diminutivus, two woodland species. Agaricus semotus can be distinguished by somewhat larger size and habitat preference, while Agaricus diminutivus is distinctive because of its unusually small size and slender stature. Except for gill color, it could easily be confused for species of Lepiota.