Summary:
Distinctive features are 1) small size, 2) a cup-shaped, bald to pruinose, striate cap that is beige, pinkish brown, gray-brown, to blackish, 3) gills radiating from the point of the stemless attachment that are buffy, pinkish-buff or brown with pale edges, the margin often translucent-striate, 4) growth on the underside of logs, 5) a white spore deposit, and 6) microscopic characters. Resupinatus striatulus is "confused in the literature with R. applicatus": for instance the majority of the collections of the two species examined in Ontario were R. striatulus, (Thorn(2)).

Cap:
0.15-0.7cm, cupulate [cup-shaped], dorsally or laterally attached; beige, pinkish brown, gray-brown, to blackish, darkening on drying; appears moist and polished when water-soaked, finely pruinose overall, or margin bald, margin translucent-striate or not, sometimes faintly sulcate [grooved], edge entire or crisped [wavy]

Gills:
"radiating from point of attachment or a central or eccentric point on underside", subdistant, moderately narrow to moderately broad; colored as cap or slightly paler, buffy, pinkish-buff, or brown, edges paler; edges entire, surface bald or atomate [with tiny shiny particles]

Stem:
absent

Microscopic spores:
spores (3.3)4.0-6.0 x (3.1)3.5-5.0 microns, round or nearly round, inamyloid, colorless; basidia 4-spored, 20-27 x 5.5-7 microns, clavate; cheilocystidia a dense fringe on gill edges, (10)15-27 x 4-8 microns, projections tapering and needle-like, often tipped with a fine droplet 1.0-1.5 microns in diameter, "and obscured by granular-crystalline yellowish encrusting material"; cap cuticle 10-25 microns deep, "a tangle of brownish hyphae, with many details obscured by heavy encrustations of yellowish granular or crystalline material", hyphae 1.5-5.5 microns wide, "with irregular knobs, branchlets, and pegs in some areas dense and repent, in others with loose ends verging on a trichoderm", gelatinous zone about 100 microns thick in cap margins, to 400 microns thick in center, colorless, "with tangled and ascendant, faintly brownish hyphae", (1.0)1.5-3.0 microns wide, clamp connections to 7 microns diameter; cap trama 45-150 microns thick, "sometimes poorly distinguished from gelatinous zone, but usually more dense, pale brown, then descending into gills" where it becomes more colorless and gelatinized, hyphae 2-6 microns wide, (Thorn); Resupinatus species have distinctive cell surface structure

Spore deposit:
white

Notes:
Resupinatus striatulus was examined from BC, MB, NB, ON, QC, NY, Germany, and the United Kingdom, and is "Probably widespread in Europe and North America", (Thorn(2)). There is a collection from MT at the University of Washington.

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