Summary:
Features include 1) effuso-reflexed, tough, leathery fruitbodies growing on oak or chestnut, 2) thin caps that are single or shingled, projecting 1-4cm from the wood, the upper surface dark red-brown, black-brown, to ocher-brown, black when old, zoned, wavy and ridged, and tomentose to bald, with the margin sharp, wavy, scalloped, and somewhat lighter in color, 3) lower surface of caps and the part of the fruitbody flat on the wood (the spore-bearing area) that is a) red-brown to orange-brown when fresh, especially toward marginal area, sometimes with a lilac tint, then dark brown to gray-brown, and b) tuberculate, undulating, not cracking much, 4) bristle-like setae visible with a hand lens on the spore-bearing surface, 5) tissue that blackens in KOH, 6) spores that are elliptic, smooth, and inamyloid, 7) the fruitbody comprised of five layers: a) a hymenium of basidia, basidioles, hyphidia, and setae 40-80(100) x (6)8-10(12) microns, projecting (20)40-60 microns, b) a setal layer, c) a hyphal layer, d) a cortex, and e) a tomentum layer.

Microscopic:
SPORES 4.5-6 x 2.5-3 microns, elliptic, smooth, inamyloid, colorless; BASIDIA 4-spored, 20-25 x 3-4 microns, cylindric-clavate, without basal clamp connection; CYSTIDIA none; SETAE 40-60 x 5-7 microns, subulate [awl-shaped], dark brown, thick-walled, "both exserted beyond the hymenium and enclosed in the trama"; HYPHAE monomitic, generative hyphae 1-2.5 microns wide, colorless, septa without clamp connections, tramal hyphae 2-4 microns wide, brown, thick-walled, rarely septate without clamp connections, (Breitenbach), SPORES (3.5)3.8-5.5 x (1.8)2-2.8(3) microns, elongated elliptic, with one side flattened; fruitbody comprised of five layers: 1) hymenium of basidia, basidioles, hyphidia, and setae, 2) setal layer, 3) hyphal layer, 4) cortex, 5) tomentum; BASIDIA 4-spored, 15-25(30) x 4-6(7) microns, clavate or subclavate, colorless or yellowish, sterigmata 4-5 microns long, basidioles 8-18 x 3.5-5 microns, without encrustation; HYPHIDIA present but usually not well differentiated, 1.5-3 microns wide, colorless or yellowish, thin-walled; CYSTIDIA absent; SETAE very numerous, 40-80(100) x (6)8-10(12) microns, projecting (20)40-60 microns, conic to fusiform, "with acute tip, straight or some with slightly curved tip, naked or very rarely enmeshed in hyphal sheaths, without incrustation"; setal layer 70-500 microns thick, "composed of overlapping rows of setae"; hyphal layer 100-500 microns, "hyphae more or less compactly longitudinally arranged"; cortex (20)40-55 microns thick, "hyphae densely parallel or interwoven, agglutinated, rust brown", but no dark line representing cortex is visible macroscopically; tomentum 50-250 microns thick, darker than hyphal layer; "hyphal system dimitic, but difference between skeletals and generative hyphae small", setal hyphae absent, generative hyphae 2-3.5 microns wide, nearly colorless, thin-walled, skeletal hyphae numerous, (2.5)3-5 microns wide, brown, thick-walled; "in context, setal stratum and hymenium crystalline matter absent", (Parmasto)

Notes:
Hymenochaete rubiginosa has been found in WA, OR, NF, ON, AL, AR, AZ, CA, CO, CT, DC, DE, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, MI, MN, MO, MS, NC, NE, NJ, NM, NY, OH, OK, PA, SC, TN, TX, VA, VT, WI, WV, Mexico, Costa Rica, El Salvador, Cuba, Argentina, Chile, Colombia, Ecuador, Peru, all countries in Europe where Quercus spp. grow, Caucasus, Japan, Russia far east, Turkey, Kenya, Morocco, South Africa, Borneo, India, Pakistan, Philippines, Vietnam, and New Zealand, (Parmasto). Literature records also exist from BC and ME, (Ginns(5)), and there are BC collections at Pacific Forestry Centre and University of British Columbia.

Synonyms and Alternate Names:
Helvella rubiginosa Dicks
Marasmius filopes Peck
Marasmius thujinus Peck