A white to whitish collybioid mushroom of conifer wood and duff that develops rusty or cinnamon spots on the cap, gills and stem as it ages. It has very crowded white gills, a firm stem with a tapered rooting base, and a bitter taste. It is the type species of Rhodocollybia.
Cap: 2-6 cm, convex with an inrolled margin, becoming broadly convex or nearly flat; dry, bald, white to whitish or pale tan, developing cinnamon spots. Gills: narrowly attached, very crowded, white, becoming rust-spotted. Stem: 5-7 cm long, 0.5-1 cm thick, equal with a tapered rooting base, bald, white, spotting rusty. Flesh: white, unchanging. Odor: sweetish or not distinctive. Taste: slightly to moderately bitter. Spore print: white to faintly pinkish in a thick print. Spores: 4-6 x 4-5 µm, smooth, subglobose to broadly ellipsoid, many dextrinoid.
