Cap 7-13 cm broad, convex when young, later plano-convex to plano-concave, often wavy in outline; margin at first incurved, then decurved, plane to raised in age, not striate; surface glabrous, subvisicd when moist, frequently with adhering debris; color dingy-cream, at maturity tinged greyish-brown; context pallid, firm, brittle, granular in texture, 2-3 cm thick, slowly vinaceous when injured, becoming grey-brown to nearly black; odor mild; taste mild to acrid.
Gills adnate, adnexed, to subdecurrent, close, moderately broad, brittle, at first cream-buff, becoming grey-brown, bruising pinkish-vinaceous, eventually grey-brown to black; lamellulae up to 3-seried.
Stipe 3-7.5 cm long, 2-4 cm thick, stout, solid, equal to subbulbous; surface faintly wrinkled, whitish when young, becoming greyish to nearly black in age; bruising vinaceous, then grey-brown to black; context white, brittle with similar color changes as the cap context; veil absent.
Spores 7.0-9.5 x 5.5-7.0 µm, subglobose to ovoid, amyloid ornamentation of warts and lines forming a partial reticulum; spore print cream.
Solitary to scattered in mixed hardwood-conifer woods; fruiting shortly after the fall rains.
In contrast to the many colorful Russula species that inhabit Bay Area woodlands, the fruiting bodies of Russula densifolia are often drab and covered with dirt and debris. Indeed, it is sometimes difficult to tell where dirt and the normally greyish-brown pigments of this mushroom begin and end. Young specimens are typically off-white to dingy-cream, but soon become tinged grey-brown to black or when bruised, vinaceous-pink, then grey-brown to black. Complicating matters, two other Russulas, R. dissimulans and Russula nigricans are very similar and not easily distinguished by inexperienced collectors. Russula dissimulans differs in having a moist to dry, not subviscid cap, and subdistant gills. Russula nigricans typically has thick, distant gills, but according to Thiers may intergrade with R. dissimulans. To identify these species with confidence, a microscope is needed as cuticle thickness and spore ornamentation are important distinguishing features. For more details, see Thier's Russula monograph in the Agaricales of California.