Summary:
Features include 1) resupinate growth on barkless conifer wood, 2) a grayish white to pale ochraceous fruitbody, the surface smooth to rarely tuberculate, 3) spores that are elliptic to fusiform or somewhat almond-shaped, thin-walled to thick-walled, and smooth, 4) basidia that are typically pleural, and 5) a monomitic hyphal system, the hyphae with clamp connections.

Microscopic:
SPORES somewhat variable in size and shape but as a rule elliptic to fusiform or subamygdaliform [somewhat almond-shaped], thin-walled to moderately thick-walled, smooth, normally 6-8 x 3.5-4.5 microns; BASIDIA cylindric, "slightly constricted, typically pleural", when fully developed usually 20-25 x 6-8 microns, 4-spored, with basal clamp connection; HYPHAE monomitic, all with clamp connections, 2.5-4 microns wide, thin-walled, "in the subiculum rather sparse, straight and fairly uniform", arranged in more or less parallel fashion, "other hyphae somewhat narrower, intermingled and agglutinated", (Hjortstam), SPORES 3-5 x 2-3 microns, even, colorless; BASIDIA 4-spored; GLOEOCYSTIDIA none; HYPHAE about 1.5-2 microns wide, densely interwoven, conglutinate, not encrusted, section not appreciably colored, (Burt)

Notes:
Aphanobasidium pseudotsugae has been found in BC, ID, and NY, but the distribution likely more extensive, especially since some authors including Liberta(2) regarded this species as a synonym of Phlebiella filicina (Bourdot) Larsson & Hjortstam, now Aphanobasidium filicinum, (which lacks clamp connections and seems to be obligate on ferns) and numerous reports of Phlebiella filicina on wood may have been based on specimens of P. pseudotsugae, (Ginns). Aphanobasidium pseudotsugae is distributed in the whole of Northern Europe but seems more frequent in the central and northern parts, (Hjortstam(6)).