Cap 50-95 mm broad, convex to plano-convex, dry, appressed-fibrillose, radially cracked and split in age, at first black to dark grayish brown overall, in age black in the center and radially streaked black over a white background. Odor of phenol. Gills free, close, broad, white to reddish brown then dark brown. Stem 35-80 x 5-15 mm, cylindrical or enlarged downwards to a subbulbous or abruptly bulbous base, glabrous, white above, brown below, with a large, skirtlike annulus near the apex. Stem base stains bright yellow where bruised. Spore Deposit dark brown. Edibility: unknown but probably poisonous.
The black cuticle on this new species of Agaricus is at first solid but splits radially as the cap expands revealing the white tissue underneath. The base of the stem turns yellow when rubbed or sliced open. It is best to avoid eating all yellow-staining species of Agaricus that have a phenol odor. Most of them cause gastrointestinal upset when ingested. Is: HA, KA.