Cortinarius brunneus, commonly called the Brown Webcap, has a dark brown, smooth to finely fibrous cap that is convex when young, later flattening. It is an ectomycorrhizal species, most often associated with conifers such as spruce and pine, occasionally with birch, typically growing in moist, acidic soils of coniferous and mixed forests.

Cap at first bell-shaped with a central bump, later becoming more convex to flattened. The surface is smooth to finely fibrillose, hygrophanous, dark brown to chestnut-brown when moist, paler cinnamon or ochre when dry, sometimes blackish with age. The margin often carries ragged whitish remains of the veil. Flesh is thin, brown, not changing colour when cut, with a mild earthy to radish-like smell. Gills adnate to slightly notched, fairly well separated and rather thick, 5–8 mm broad. They are cinnamon-coloured at first, later becoming umber to rusty brown, with an entire edge. Stem slender to club-shaped, sometimes hollow with age. It is dark brown, often paler near the top, and may show a faint ring zone or zones of veil remnants. The surface can be finely fibrillose, with whitish zones from the universal veil. Spore print cinnamon to rusty brown.

Microscopic Features: Spores broadly ellipsoid, ornamented with coarse warts, measuring 8–10 × 5–6 µm, dark brown under the microscope.