Summary:
Distinctive features are a slightly viscid chestnut brown to vinaceous-brown, often two-toned cap, often eroded gills, a rooting stem, a tendency to develop reddish brown stains on gills and stem, a strong almond odor, and fruiting around old stumps and in lignin-rich humus.

Cap:
4-10cm across, broadly convex to flat; deep chestnut-brown to vinaceous brown or reddish brown at center, often paler or pinker or redder toward margin and gradually fading overall when old; "slightly viscid when moist but soon dry", (Arora), 4-10.5cm across, generally at least 7cm, convex to hemispheric, becoming flat and broadly but shallowly umbonate; subhygrophanous [somewhat hygrophanous], dark vinaceous brown or chestnut brown at center, "fading gradually and then abruptly towards the margin, warm buff to pale tawny there", the colors losing their warm tones in fading while drying; subviscid when moist, bald or occasionally minutely fibrillose on disc, sometimes obscurely silvery-spotted on drying, (Lennox)

Flesh:
thin; "white or reddish-stained", (Arora), rather thick centrally, up to 1cm, tapering evenly and very thin at margin, not tough, firm-brittle when moist; pallid, (Lennox)

Gills:
adnexed, notched, or seceding, crowded; creamy or pale yellow to buff to pale orange, often reddish-stained when old; edges sometimes overlapping each other and eroded when old, (Arora), sinuate-uncinate, crowded, 84 reaching stem, broad, 2.8-3.9 x 0.5-0.6cm, ventricose, blunt near stem and sharp near cap margin, thin, 3 tiers of subgills; white to pale orange, yellowing in drying, frequently stained ferruginous, edges colored as faces; "serrate to even when young, strongly eroded and fraying later", sometimes minutely transversely striate, (Lennox)

Stem:
6-20(30)cm x (0.5)0.8-2cm, "usually quite long and deeply rooted", equal in upper part or swollen slightly near ground level, tapered gradually below to a point, solid or hollow when old; whitish, but usually developing reddish to reddish brown stains especially over the lower part; dry, (Arora), 6.5-20(30)cm x 0.5-2cm, equal in upper half but inflated slightly in lower half and then narrowing abruptly into a pseudorhiza-like prolongation, buried for half its length "and covered there with pieces of rotten wood", solid to somewhat hollow, fibrous, becoming frayed and splitting, flexuous [wavy]; "white but staining ferruginous, especially towards base"; powdery-pruinose at top, bald in lower part, strongly striate-grooved, without rhizomorphs, (Lennox)

Odor:
heavy sweet benzaldehyde or almond extract, (Arora), strong almond or benzaldehyde, (Lennox)

Taste:
somewhat bitter, (Arora), faint and unpleasant or none (Lennox)

Microscopic spores:
spores 6-8 x 3.5-5 microns, elliptic, smooth, some dextrinoid, (Arora), spores 6-8 x 4-5 microns, ovate, smooth, with dextrinoid endosporium or cytoplasmic contents that are frequently retracted from the apicular end, thin-walled to thick-walled, colorless; basidia 2-spored and 4-spored, 26-30 x 5-6 microns, "with dextrinoid endosporium which retracts into the upper or lower half of the basidium and creates a septate appearance"; pleurocystidia and cheilocystidia absent; cap cuticle a gelatinized layer 50-75 microns thick, composed of interwoven hyphae, with a few projecting hairs, overlying a zone of radial, tubular hyphae 4-8 microns wide, (Lennox)

Spore deposit:
whitish to buff (Arora), pale orange (Lennox)

Notes:
Rhodocollybia oregonensis was examined from WA and ID, (Lennox). It has been found in CA (Arora). There are collections from BC and OR at the University of British Columbia.

EDIBILITY

unknown (Arora)

Synonyms and Alternate Names:
Collybia oregonensis A.H. Sm.