Summary:
Features include small size, bright orange, striate cap that fades along the margin to whitish, white gills gradually tinged with yellow, white stem that is yellowish at base, and growth under Douglas fir and pine. Maas Geesteranus gives the -us ending for the species (aurantiidiscus), presumably regarding it as a noun. The description is derived from Smith except where noted.

Cap:
0.7-2cm across, bluntly to broadly conic, margin appressed against the stem when young and flaring slightly when old; orange when young ("mikado orange"), fading to yellowish ("mustard yellow") on disc and whitish along margin; bald, striate when moist^, (Smith), conic to bell-shaped, umbonate, not expanding, (Maas Geesteranus)

Flesh:
thin, fragile; orange to yellow

Gills:
adnate to slightly hooked, close to subdistant (20-24 reaching stem), narrow to subventricose [slightly broader in the middle]; white, tinged with yellow when old, edges colored as faces

Stem:
2-3cm long and 0.1cm wide, equal, straight, fragile, hollow; white in upper part, yellowish at base; base is scarcely fibrillose [slightly covered in fine fibers], top of stem faintly pruinose

Microscopic spores:
spores 7-8 x 3.5-4 microns, elliptic, inamyloid, [presumably smooth]; basidia 4-spored, 20 x 6 microns; pleurocystidia and cheilocystidia similar, 38-47 x 5-14 microns, "fusoid with a long narrow neck, smooth in mounts of fresh material", often having the neck or tip incrusted with an amorphous mass in mounts of revived material, colorless; cap trama with poorly differentiated pellicle, the tissue beneath it homogeneous or the upper part composed of only slightly enlarged hyphae, faintly vinaceous brown in iodine

Spore deposit:
[presumably white]

Notes:
It is found at least in WA, OR, and ID (Smith), and is frequent on foray lists from BC. There are collections from BC at the Pacific Forestry Centre and the University of British Columbia.

EDIBILITY

Synonyms and Alternate Names:
Mycena aurantiidisca Murrill