Summary:
Peniophora rufa may be recognized on sight by 1) occurrence on fallen aspen and other Populus limbs and logs, and 2) small vinaceous to red pruinose fruitbodies with the surface gyrosely wrinkled. Microscopic characters include 3) spores that are suballantoid, smooth, colorless, and white to pale red in spore print, 4) cystidia of 2 types: apically encrusted cystidia with the basal part thin-walled, and sulfo-positive gloeocystidia with granular contents, thick walls, and often an outer layer of crystals, and 5) a monomitic hyphal system, the hyphae densely branched and intertwined, with clamp connections.

Microscopic:
SPORES 7-9 x 2.5-3 microns, suballantoid, spore print pale red; BASIDIA 4-spored, 40-50 x 5-6 microns, clavate, with basal clamp connection, "basal part prolonged and interwoven", CYSTIDIA of 2 types: 1) numerous, small, apically encrusted cystidia, the encrusted part 10-12 x 5-6 microns, the basal part thin-walled, 2) sulfocystidia "of varying size, generally large, reaching a length of 200 microns" and a width of 20-25 microns, with granular contents, thick gelatinous walls, and often an outer layer of granular crystals, "larger cystidia emanating like pseudocystidia from the subicular layer", "with the thickening of the subhymenium, smaller sulfocystidia with thinner walls appear"; HYPHAE monomitic, with clamp connections, densely branched and intertwined, hyphae next to the substrate 3-4 microns wide, brown, and not swelling in KOH, those of the main part of the fruitbody colorless, swelling more or less, 5-8 microns wide or even more, "often with a grainy layer of crystals on the surface", hymenial hyphae 2-3 microns wide, thin-walled, not swelling, (Eriksson), SPORES 6-8.5 x 1.5-2 microns, cylindric, curved, smooth, colorless, GLOEOCYSTIDIA numerous, spore deposit white, (Lincoff), spores 6-8 x 1.5-2 microns, "even, curved", deposit white; GLOEOCYSTIDIA 50-90 x 7-10 microns, flexuous [wavy], "scattered in or near the hymenium but not protruding"; hymenium 1000-2000 microns thick at center, 600-800 microns thick in marginal part, composed of ascending, loosely interwoven, encrusted, colorless hyphae 4-4.5 microns wide over the encrustation, (Burt)

Notes:
Peniophora rufa has been found in BC, OR, ID, AB, MB, NB, NF, NS, NT, ON, PE, PQ, SK, YT, AK, AZ, CO, IA, MA, ME, MI, MN, MT, ND, NE, NH, NM, NY, PA, VT, WI, and WY, (Ginns). Its distribution includes NF to MA and westward to ND and CO, (Burt). It occurs in Finland, Norway, and Sweden, (Eriksson). It is reported from WA by Andrew Parker, pers. comm.

Synonyms and Alternate Names:
Cyphella conglobata Burt