Cap 6-11 cm broad, obtuse-conic, expanding to plano-convex to plane with or without a low umbo; margin at first incurved, then decurved to level, occasionally wavy; surface blackish-brown to dark-brown at the disc, sometimes with a satiny sheen in youth, elsewhere lighter brown, overlain with dark radial fibrils, at times fibrillose; context whitish, greyish-black beneath the cuticle, unchanging, soft, relatively thin, up to 1 cm thick; odor mild, taste mild to slightly of radish.
Gills free, close, up to 2 cm broad, arcuate, whitish in youth, dingy-pink in age, edges even, marginate, colored grey-brown; lamellulae in up to five series.
Stipe 5-12 cm long, 1.0-2.5 cm thick, round, solid, fleshy-fibrous, equal to slightly enlarged at the base; surface of appressed grey-brown fibrils over a pallid background; veil absent.
Spores 5.5-8.0 x 4.0-5.0 µm, broadly elliptical to oblong-elliptical in face-view, similar in profile but inequilateral with a straight and curved side, smooth, thin-walled, hilar appendage not conspicuous; pleurocystidia fusoid-ventricose with horned apices; cheilocystidia, thin-walled, clavate; spore print pinkish-tan.
Solitary to scattered on conifer stumps, logs, wood-chips, and sawdust piles; fairly common in the San Franciso Bay Area on Monterey pine (Pinus radiata); fruiting fall to mid-winter.
Edible according to the literature, but untried locally.
Fieldmarks of Pluteus atromarginatus are a dark-brown often slightly umbonate cap that fades to greyish-brown, the surface streaked with dark fibrils, and free gills with brown edges, i.e. marginate. It is sometimes confused with Pluteus cervinus, with which it was once considered a variety or subspecies, but the latter has a uniformly brown, not streaked cap, lacks marginate gills, and is more common on hardwoods than conifers. Though rarely collected for the table, it should be noted that some Entoloma species, many of which are toxic, are similar in stature and also have pink spores. They can be distinguished by attached gills, a terrestrial, not lignicolous habit, and angular spores.