Regarded as NT in the Norwegian Red List (2021). Growing on fallen needles, small twigs and cones, or among moss under Picea, often in fairly wet, fern rich places. Also found among fallen leaves under Alnus. Summer to autumn. Rare. Known from Finland, Norway, Sweden, France and Germany (Aronsen & Læssøe 2016).

Pileus 2 - 10 mm across, conical to campanulate or parabolical, becoming convex with age, often with a small papilla, translucent-striate, hygrophanous, delicately pruinose, glabrescent, bright orange with yellow shades, more yellow with age, but with orange centre. Lamellae 7 - 10 reaching the stipe, ascending, broadly adnate, decurrent with a tooth, pale yellow or whitish with bright yellow edge. Stipe 15-60 x 0.3-0.5 mm, straight to somewhat curved or flexuous, terete, fragile, entirely puberulous, glabrescent except for the apex, orange, more brightly coloured at the apex, attached to the substratum by radiating, fine, yellow to yellowish-white fibrils. Flesh very thin and fragile. Odour none.

Basidia 22-28 x 5-6 µm, slender-clavate, 2-spored, with sterigmata up to 7 µm long. Spores 6.6-9.8 x 3.3-5.5 µm, q 1.6-2.3, qav 1.9-2.0, pip-shaped, smooth, non-amyloid. Cheilocystidia 13-68 x 7-17 µm, fusiform, lageniform, utriform, subcylindrical, clavate, with broadly rounded apex, smooth, sometimes with one or two outgrowths, with yellow contents. Pleurocystidia similar, not frequent. Lamellar trama not vinescent in Melzer's reagent. Hyphae of the pileipellis 2-8 μm wide, covered with simple to furcate, cylindrical, fairly coarse excrescences 2- 15 x 1-4 μm, sometimes the excrescences are cystidia-like, fusiform to lageniform, up to 40 x 8 μm, terminal cells smooth to diverticulate. Hyphae of the cortical layer of the stipe 2-3 µm wide, smooth, terminal cells (caulocystidia) numerous, in tufts, 13-70 x 7-22.5 µm, globose, ellipsoid, fusiform, subcylindrical, with yellow contents. Clamp connections absent.

More microscopic figures.

Maas Geesteranus (1990) described Mycena oregonensis as 4-spored and with clamp connections, based on American material. He also stated that European collections have shown to be 2-spored and devoid of clamps. While Ronikier (2003) confirmed the absence of clamp connections in two Polish collections, Robich (2003: 533-534) claimed that clamps were present at the hyphae of the pileipellis and the cortical layer of the stipe in Italian material.

Mycena strobilinoides Peck, an American species reported by Robich from Italy and from Switzerland by Métrod, looks similar with it's orange cap. It differs, however, among several features, by the cheilocystidia which are densely covered by excrescences, and by the diverticulate hyphae of the cortical layer of the stipe and the terminal cells that are equally diverticulate. Mycena acicula (Schaeff.) P. Kumm. also has an orange-red pileus. The colour, however, usually is more red and it fades to more yellowish. Besides, it differs microscopally. The hypoderm is built up by globose to subglobose cells, while they are elongated in M. oregonensis. The hyphae of the cortical layer of the stipe in M. acicula are covered with coarse excrescences embedded in gelatinous matter, but they are smooth and dry in M. oregonensis. The cheilocystidia and the caulocystidia have no yellow contents in M. acicula. Mycena oregonensis is the monotype of section Oregonenses Maas Geest.