CAP 3–6 (10) cm across, conic at first, expanding to broadly conical to bell-shaped; with a distinct umbo. Margin incurved at first, becoming wavy and uneven. Surface smooth, slimy to thinly viscid when wet; hygrophanous, fading when dry. Golden to smoky tan when young, occasionally two-toned, with a darker brown disc and paler margin, soon darkening to chestnut-brown or cocoa- brown, and sometimes with grayish tones in age. GILLS narrowly attached to nearly free, close to crowded, moderately broad. Smoky white to light cinnamon when young, developing cinnamon color as spores mature, to dull cinnamon in age. STIPE 3–7 cm long above ground, 20 cm overall, 0.8–1.5 thick at apex, equal or tapered downwards, pseudorhiza equal with stipe for about half of its length, then tapered to a slender ‘root’. Surface dry to lubricous, smooth or with scattered fibrils, finely longitudinally lined. Ivory to tan, occasionally with a pinkish cast near apex, transitioning to a red-orange to orange-brown color at ground level; darkening from the base up in age. Pseudorhiza dark red-brown, staining red- orange to maroon. FLESH very thin, somewhat cartilaginous, off-white to tan. Stipe solid, stuffed with fibrillose pith. Pith whitish to pale tan, staining tan, rind concolorous with exterior. ODOR indistinct to slightly floral. TASTE indistinct. SPORE DEPOSIT dark cinnamon brown to dark red-brown. MICROSCOPY: Spores (8) 9–10 (11) x 5.3–6 (7) μm, averaging 9.6 × 5.7 μm, amygdaliform, with an ec- centric apiculus and small, smooth beak in side view, punctate to roughened, amber in KOH. Basidia 30–40 x 6–9 μm, clavate, with a rounded upper portion, 4-spored. Cheilocystidia 20–35 μm long, 2–3 μm wide, abundant, thin-walled, hyaline. Highly variable, and often in a fused mass; difficult to separate into isolated ele- ments when studying dried materiel. Variably clavate, cylindrical or inflated, with rounded to pointed heads, often with thread-like extensions in age. Pleurocys- tidia absent. Cap cuticle a two-layered ixocutis; upper layer ~400 μm thick, uplifted, highly gelatinized, hyaline hyphae, 1–2 μm wide; loosely embedded in a gelatinous matrix. Lower layer; wider (4–7 μm) gelatinized hyphae, with dull orange-brown diffused pigments. Clamp connections absent.
ECOLOGY: Ectomycorrhizal with conifers; sites in California have Douglas-fir (Pseudotsuga menziesii), White Fir, (Abies concolor), and Western Hemlock (Tsuga heterophylla). Oregon sites are dominated by Western Hemlock and Sitka Spruce (Picea sitchensis). This species is likely restricted to mature and old-growth forests. Fruiting in small to large clusters (rarely solitary) in soil, typically in areas with thick duff. Fruiting in fall.
SIMILAR SPECIES: Phaeocollybia olivacea has an olive-green cap, and yellowish green gills and stipe apex, as well as coarsely roughened spores with a longer beak. Phaeocollybia spadicea has a darker brown to gray-brown cap that develops vinaceous tones in age. It also has darker gills, slightly smaller spores (8 × 5 μm), and tibiiform to lageniform cheilocystidia with narrow, thick-walled necks.