Summary:
Features include 1) a hygrophanous, brownish orange cap that is conic becoming flat or almost flat with a low umbo, 2) young gills often with a lilac tinge, 3) a stem that is stuffed to hollow, cartilaginous, shiny, and tan, 4) a root-like pseudorhiza that often turns suddenly laterally under the soil, becoming a thin, black-brown, brittle extension which may extend more than a meter away from the fruitbody, 5) a radish-like, slightly fishy, or floral odor with complex undertones, 6) an unpleasant, often bitter taste, and 7) microscopic characters including beaked, roughened, lemon-shaped spores, a cap cuticle without a distinct gelatinous trichodermium, and a lack of clamp connections. Phaeocollybia attenuata is neither common nor rare.

Cap:
occasionally reaching 5cm across, conic-campanulate with incurved outer margin, often with acute papillate umbo when young; hygrophanous, either uniformly brownish orange or zonate with slightly darker brown disc, yellow-brown to orange-brown margin and pale yellow-brown edge, when dried dark red-brown and matte; moist to lubricous, bald, edge often striatulate [finely striate], (Norvell(11)), 1.5-5cm across, obtusely conic to broadly bell-shaped; hygrophanous, orange brown to tawny; lubricous, bald, edges rarely striatulate [finely striate], (Castellano), 1.5-5cm across, obtusely conic, becoming broadly umbonate or broadly conic to flat when old, the margin inrolled at first and when old often wavy; hygrophanous, "amber-brown" when moist or near "ochraceous-tawny", fading to "ochraceous-buff" or "warm-buff" (pale yellow), often spotted amber-brown when old; lubricous, bald, polished, "the margin seldom striatulate at any stage", (Smith(43)), orangish brown to tawny, darkening when old, moist to viscid, smooth, (Trudell)

Flesh:
0.1-0.2cm thick on umbo, cartilaginous pliant; at first pallid, becoming duller and darker when old, (Norvell(11), thin but cartilaginous; buff to watery brown, (Smith(43))

Gills:
"pinkish buff to lilac-colored when young, becoming moderately pinkish brown and aging to dark orange brown", (Norvell(11)), attached by decurrent tooth, nearly free when old; pale pink-tan at first, "occasionally faintly blue to violaceous tinged", (Castellano), attached by a tooth, nearly free when old, close, narrow, equal; pallid to dingy vinaceous-biff, and at times with a faint caesious tinge at first, pale cinnamon-brown when old and with darker rusty-brown spots; edges even, (Smith(43)), young gills tend to be bluish to lilac-tinged (L. Norvell, pers. comm.)

Stem:
up to 7cm above ground, combined with pseudorhiza about 22cm, 0.2-0.5cm wide at top, central to slightly eccentric [off-center], equal, "cartilaginous when young and pale, soon corneous after darkening", initially stuffed but becoming hollow when old; at first pale yellowish brown, later gradually ferruginous from the ground upwards, often a narrow deep orange-brown band separating the pale yellowish brown at top from the darker lower part until the entire stem ages to dark reddish brown, pseudorhiza lateral-monopodial, cartilaginous upper part continuous with reddish brown lower stem, gradually tapering to thin, brittle, brownish black extension, the wire-like lower part often bending sideways below the cartilaginous part, (Norvell(11)), up to 20cm long, only 0.5cm wide at top, more or less equal; cartilaginous, stuffed at first becoming hollow; pseudorhiza long, thin, wire-like, black-brown, (Castellano), 10-12cm x 0.3-0.5cm, equal above a long (3-8cm) pseudorhiza, hollow, very cartilaginous; at first pallid brownish overall, dark rusty brown to blackish when old; bald, polished, (Smith(43)), pseudorhiza lateral-monopodial, meaning that when pseudorhiza is followed downward toward its origin, there is often a sudden lateral turn, after which the thin, brittle, wire-like thread runs laterally, often for a distance greater than 100cm from the fruitbody, (Norvell(6))

Veil:
veil remnants inconspicuous, evident as sparsely distributed, short, fibrillose patches on stem apex, (Norvell(11))

Odor:
variably strong to not distinctive, radish-like, slightly fishy smelling, or floral (like pansies) with complex undertones (similar to boiled potatoes or burnt hair), (Norvell(11)), strong and radish-like (Smith(43))

Taste:
"slightly to strongly disagreeable, often bitter", (Norvell(11)), becoming very disagreeable, often slowly, (Smith(43))

Microscopic spores:
spores 7-10 x 4.5-7 microns, average 9 x 5.75 microns, broadly ovate to amygdaliform [almond-shaped] in face view, subglobose-limoniform [nearly round to lemon-shaped] with a prominent central apical beak (up to 2.5 microns wide and long) and short narrow apiculus in side view, rugulose-warty [wrinkled-warty] except over smooth apiculus and beak, the warts dark brown in KOH or water; basidia 4-spored, 25-34 x 5-7 microns, colorless; pleurocystidia absent, cheilocystidia "abundant, but often collapsed together in an agglutinated barrier, filamentous to narrowly clavate", variable in length but usually 20-30 microns long, 2-3.5 microns wide; cap cuticle a two-layered ixocutis with thin (25-50 microns) suprapellis of radially aligned, 40-60 x 1-2 microns, gel-incrusted, colorless to pale orange-yellow hyphae overlying 100-300 microns thick, pale to dark orange-brown subpellis of inflated, 4-8 microns wide, subgelatinous hyphae with intraparietal pigments; tibiiform diverticula "abundant on mycelia and primordial and pseudorhizal pelli, frequent on vestiges of pellicular veil on stipe apex, rarely present on pileipellis; clamp connections absent, (Norvell(11)), "spores 7-8.5 x 5-5.5 microns, limoniform-round with a pronounce apical beak, coarsely ornamented; basidia 4-spored; cheilocystidia broadly clavate and packed in a dense gelatinous barrier at the gill edge; cap cuticle "subgelatinized radially arranged hyphae, dingy ochraceous", lacking an extensive colorless gelatinous matrix; clamp connections absent, (Castellano), spores 7-9.5 x 4.5-5.5 microns, broadly ovate in face view, broadly inequilateral and with a short pale beak in side view, distinctly roughened, tawny in KOH; basidia 4-spored, 24-28 x 6-7 microns, colorless in KOH or nearly so; pleurocystidia none, cheilocystidia clavate and resembling miniature basidia (colorless, smooth, thin-walled), or rarely a few filaments about 1.5 microns wide present; cap cuticle consisting of "radially arranged subgelatinous hyphae dingy ochraceous in KOH", that is, without the distinct gelatinous trichodermium that is common in Phaeocollybia; clamp connections absent, (Smith(43))

Spore deposit:
deep reddish brown (Norvell(11)), black-brown [sic] (Castellano)

Notes:
It is found in BC, WA, OR, CA, (Norvell(6)). It was known from about 80 existing localities (Norvell(11)). Distribution is west of the Cascade and Sierra Mountains from southern BC to northern CA: it is most often recorded from OR coastal forests, (Norvell(11)).

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