Summary:
Features include 1) growth flat on wood, 2) a fruitbody that is cinnamon to dark brown or reddish brown, smooth becoming cracked, 3) bristle-like setae visible with hand lens on surface, 4) spores that are short cylindric, smooth, inamyloid, and colorless, 5) the fruitbody with three layers: a) a hymenium (outer layer) with basidia, basidioles, and setae, (no hyphidia or cystidia), b) a setal layer with 1-10 rows of setae, and c) a hyphal layer, (next to substrate: cortex and tomentum are not present). In contrast to most species of Hymenochaete, only about a half of the specimens of H. cinnamomea studied have numerous spores (less than that in most Hymenochaete species), (Parmasto(1)). The Parmasto(1) description here is for subspecies spreta.

Microscopic:
SPORES 4.5-6.5(7) x 1.8-2.8(3.2) microns, short cylindric, some slightly curved, or almost elliptic with one side flattened; FRUITBODY consists of 3 layers: 1) hymenium with basidia, basidioles, and setae, (no hyphidia or cystidia), 2) setal layer, 3) hyphal layer, (cortex and tomentum are not present, and there is no dark line representing cortex); BASIDIA 4-spored, 15-30 x 3.8-6 microns, subclavate or subutriform, sometimes with thickened basal walls, sterigmata 4-5 microns long, basidioles 15-30 x 3.5-5 microns, septate, "usually yellowish, later walls often thickened at base, yellow or brownish and granulose", basidioles may simulate thick-walled hyphidia; SETAE numerous, (60)70-120(150) x 5-9(10) microns, projecting to 90 microns, subulate [awl-shaped], "usually some slightly curved, naked or enmeshed in hyphal sheaths, without incrustation, tips acute or very sharp", "hyphae between setae vertically arranged, short-celled"; setal layer has 1-10 more or less distinct rows of setae, sometimes between the rows there is a thin intermediate hyphal layer up to 30(60) microns thick composed of densely, sometimes partly loosely interwoven hyphae; basal hyphal layer 20-150(250) microns thick, lighter in color than setal layers or the same color, hyphae loosely arranged and interwoven; HYPHAE monomitic, setal hyphae absent, generative hyphae 2-4.5 microns wide, distinct, "yellow to brownish, with thickened walls, branches diverging at a right angle, with numerous septa"; in hyphal layer, setal layer, and hymenium, crystalline matter absent, (Parmasto, subspecies spreta), SPORES 5-7.5 x 2-3 microns, cylindric-elliptic, smooth, inamyloid, colorless; BASIDIA 4-spored, 12-20 x 3-5 microns, cylindric-clavate, with basal clamp connection (although illustrated without clamp connection); CYSTIDIA none; SETAE 55-95 x 5-7 microns, "pointed, thick-walled, brown, both exserted beyond the hymenium and enclosed in the trama"; HYPHAE monomitic 2.5-5 microns wide, thin-walled to thick-walled, brown, richly branched, without clamp connections, (Breitenbach, presumably subspecies cinnamomea)

Notes:
Hymenochaete cinnamomea subsp. spreta has been found in BC, WA, OR, ID, MB, NF, NS, ON, PQ, YT, AK, AL, AZ, CA, CO, CT, DC, FL, GA, IL, IN, KS, KY, LA, MA, MD, MI, MN, MO, MS, MT, NC, ND, NE, NH, NJ, NM, NY, OH, PA, SC, TN, UT, VA, VT, WI, WV, Greenland, and Mexico, (Parmasto(1)). Subspecies cinnamomea is found in Cuba, Argentina, Brazil, Colombia, Ecuador, Europe (common in all countries), Macaronesia, Northern Africa, West-Central and East Tropical Africa, Southern Africa, Israel, Caucasus, Middle Asia, Siberia, Russian Far East, Turkmenistan, China, Japan, and New Zealand, (Parmasto(1)).

Synonyms and Alternate Names:
Sclerotinia caricis-ampullaceae Nyberg