Fruiting body fan to kidney-shaped, sessile to sub-stipitate, if the latter then lateral in attachment; cap 2.5-10.0 cm broad, 2.0-5.0 cm in width, i.e. from margin to disc; cap at first convex with an incurved, wavy margin, in age plane to slightly upturned; surface of margin glabrous, buff to dingy-tan, becoming dark-brown to vinaceous-brown towards the disc, the latter typically matted-tomentose to hirsute; context up to 0.5 cm thick, white, soft; odor indistinct; taste latently acrid.
Gills radiating from the basal attachment point, subdistant, buff-colored in youth, pale-tan in age, edges serrate; lamellulae in five to six series.
Stipe when present, very short, densely velutinate, light-brown.
Spores 5.0-6.5 x 4.0-5.0 µm, broadly elliptical to oval in face and side-view, smooth, thin-walled, verrucose, hilar appendage inconspicuous, amyloid; spore print white.
Solitary or in small groups on downed wood of montane conifers, especially lodgepole pine (Pinus contorta) and red fir (Abies magnifica); fruiting during the spring snow melt; common.
Inedible; unpleasant taste.
This snowbank species resembles the common oyster mushroom, Pleurotus ostreatus, but can be distinguished by serrate gills, a spring fruiting habit on conifer wood, and an acrid taste. Oyster mushrooms, while present in montane regions of California, fruit mostly in the fall on hardwoods. Lentinellus ursinus is a closely related species of coastal forests. It differs in having more closely spaced gills and smaller, globose spores.