Summary:
Subgenus Dermocybe. Features include 1) hemispheric to umbonate cap that is blackish red at center, in other parts brownish red, 2) close to medium spaced dark red gills, 3) cylindric to narrowly clavate stem that is buff pink to dark red, 4) radish-like odor and taste, and 5) microscopic characters. The description is derived from Niskanen(5).

Cap:
1.0-3.0cm, hemispheric to obtusely umbonate, then almost flat with downcurved margin; blackish red at center, "in other parts brownish red", "often watery streaked and zoned but not truly hygrophanous"; "really faintly tomentose-fibrillose"

Flesh:
watery and colored as cap surface in the cap, where faded lighter red, in stem "apex pale reddish or pinkish white, otherwise light red but darker, watery red below, rich dark red to blackish red along cortex in base", "pith pale reddish white"

Gills:
"close to medium spaced"; "deep red to very dark red"

Stem:
2.5-5.5cm x 0.3-0.5cm at top, 0.4-0.7cm wide at base, cylindric to narrowly clavate, stuffed to hollow; "at first buff pink with some reddish (light to pale pinkish vinaceous) fibrils, soon (or sometimes from beginning) with dark red colors, especially on base, but base proper with pale ochraceous to buff tones, sometimes colors more ferruginous red, sometimes apex orange fibrillose"; basal mycelium "presumably orange"

Veil:
universal veil "mostly evanescent, red"

Odor:
gills radish-like

Taste:
cap flesh radish-like

Microscopic spores:
spores 7-8.4(9) x 4.1-5 microns, elliptic, distinctly verrucose; basidia 4-spored, pinkish in KOH; cap cuticle surface hyphae 4.5-11.1(15-18.5) microns wide, cylindric to broadly cylindric, "pinkish to purplish or slightly brownish, some containing red pigment, some slightly encrusted, no well differentiated subcutis"; gill trama "regular, parallel interwoven hyphae, in KOH pale pinkish to colorless, some slightly encrusted, wall refractive, cylindrical to inflated", 5-26 microns wide, clamps present

Spore deposit:
[presumably a shade of brown]

Notes:
Cortinarius birkebakii collections cited in the original description were from BC, WA, and OR.

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