Summary:
Subgenus Dermocybe. 1) A characteristic feature is the tendency of the cap to lose moisture and fade from dark reddish brown (often with some olive tones) to olive-brown (subhygrophanous). 2) The most striking characteristic when present is microscopic: the presence of bluish to bluish purple particles of pigment in the hyphae of the cuticle and subcuticle of cap when mounted in KOH. Other features include 3) broad gills that are ochraceous when young, 4) a dry, equal stem that is yellowish to ochraceous when young with a covering of ocher brown fibrils, darkening to more ocher brown as it ages, 5) a sometimes bitter taste, and 6) a reddish brown cap reaction with KOH.

Cap:
(1)2-4cm across, obtuse to convex, becoming broadly convex to flat, margin incurved to decurved [downcurved]; subhygrophanous [somewhat hygrophanous], dark brown to dark cinnamon, often fading as it dries to olive brown; fibrillose, moist, more or less opaque

Flesh:
in cap olive when moist, ochraceous faded, in stem rusty ochraceous to the base, in base orange-fulvous to dark fulvous

Gills:
"adnexed, close, broad"; rusty ochraceous becoming ferruginous, then orange-ochraceous to orange-fulvous, (Ammirati), broadly attached "or with a slight notch and a decurrent tooth", "closely spaced"; yellowish brown to ocher-brown when young, "becoming more ocher-orange as spores mature", (Siegel)

Stem:
4-7cm x 0.5-1cm, equal or nearly equal, "near rusty ochraceous and darkening (more ochraceous) from the base upward, with a covering of ochraceous fibrils", (Ammirati), 3-8cm x 0.5-1.0cm, "more or less equal, or with a slightly enlarged base", "stuffed with pith when young, soon becoming hollow"; "Yellowish to yellowish buff with darker, ocher-brown fibrils, darkening more toward ocher-brown as it ages, basal mycelium pale creamy yellowish, staining dingy yellowish when handled"; "dry, covered with silky longitudinal fibrils", (Siegel)

Veil:
sparse cortina "of pale ocher-brown fibrils, leaving silky fibrils on the stipe, or disappearing altogether", (Siegel)

Odor:
not distinctive (Ammirati), indistinct (Siegel)

Taste:
more or less bitter (Ammirati), indistinct (Siegel)

Microscopic spores:
spores 7-9 x 4.5-5.5 microns, elliptic to ovate, verruculose [finely warty], in KOH brownish to pale fulvous, in Melzer''s reagent light yellowish to yellowish brown; basidia 4-spored, 24-35 x 5.5-7 microns, "clavate to more or less ventricose, thin-walled", in KOH colorless to pale vinaceous "or containing particles and masses of deep red to vinaceous red pigment", in Melzer''s reagent light yellow "or containing yellowish, brownish, orange, or reddish orange particles"; pleurocystidia absent, cheilocystidia 8-17 x 6-8 microns, "clavate to broadly clavate, thin-walled", in KOH and Melzer''s reagent similar to basidia; clamp connections present throughout the fruiting body, (Ammirati), spores 7-9 x 4.5-5.5 microns, elliptic, minutely roughened; cells of cap surface with bluish particles in KOH, (Siegel)

Spore deposit:
rusty brown (Siegel)

Notes:
Cortinarius idahoensis has been found at least in ID and WA, (Ammirati), and BC (collections by O. Ceska at University of British Columbia). The accompanying photo by Noah Siegel was taken in CA.

EDIBILITY

Synonyms and Alternate Names:
Dermocybe idahoensis (Ammirati & A.H. Sm.) Ammirati