Summary:
{See also Stereum Table.} Features include 1) growth on conifers, in resupinate form, or bent outward to form narrow shelf, or distinctly cap-like, 2) when present, caps that are shingled, wavy, and lobed, with the upper surface finely hirsute-tomentose, undulating, concentrically zoned, and colored whitish, orange, reddish brown, or dark brown, the margin whitish, 3) a spore-bearing area that is smooth to tuberculate-wrinkled, coloured beige to buff or ocherish, often with hint of violet, (margin lighter), quickly turning blood red when injured, and bleeding when cut, 4) spores that are elliptic-cylindric, smooth, amyloid, and colorless, 5) pseudoacanthohyphidia, thick-walled cystidia filled with an oily to granular, pale brown content, and presumably sharp-tipped hyphidia, and 6) hyphae of 2 types both simple-septate (lacking clamp connections): a) thin-walled to thick-walled, in the hymenium, b) thick-walled in tomentum, cortex and trama. |Stereum ostrea, Stereum rugosum, and Stereum sanguinolentum are members of the subgenus Aculeatostereum which have pseudoacanthohyphidia: thin-walled hymenial elements that bear a few (2-5, rarely up to 10) apical projections (also known as pseudoacanthophyses, aculeate-tipped basidioles, acanthocystidia, and acanthohyphidia, by different authors, the last term also used for acanthophyses - with projections throughout their length - that occur in subgenus Acanthostereum not found in North America), (Chamuris(3)).

Microscopic:
SPORES 6.5-7.5 x 2.5-3 microns, elliptic-cylindric, smooth, amyloid, colorless; BASIDIA 2-4-spored, 40-50 x 5-7 microns, narrowly clavate, without basal clamp connection; PSEUDOACANTHOHYPHIDIA 30-40 x 2-3.5 microns, thin-walled, with knob-like to thorn-like tips, CYSTIDIA "none, but ends of conducting hyphae emerging from the skeletal hyphae", 6-8 microns wide and up to over 250 microns long, fusiform, thick-walled, with brown-reddish contents; HYPHAE dimitic, generative hyphae 1.5-3.5 microns wide, thin-walled to thick-walled, septa without clamp connections, skeletal hyphae up to 8 microns wide, thick-walled, without septa, (Breitenbach), SPORES (6)7-10 x (2.5)3-4.5 microns, narrowly elliptic to cylindric, often slightly bent, smooth, amyloid, thin-walled; BASIDIA 4-spored, 25-40 x 5-6 microns, elongate-clavate; PSEUDOACANTHOHYPHIDIA 30-40 x 3-5 microns, projecting beyond the basidia; PSEUDOCYSTIDIA "thick-walled, except for in the apical part, projecting very slight [sic] above the basidia, filled with an oily to grainy, pale brown content, hyaline in the hymenium, in the basal part yellowish and 3-6 microns wide, in the upper part 4-10 microns wide, usually longer than 100 microns"; HYPHAE monomitic with 2 types of simple-septate hyphae, "hymenial hyphae thin to thick-walled, 2-6 microns wide, in the tomentum, cortex and trama thick-walled hyphae, hyaline to pale brown and 3-6 microns wide", (Eriksson), SPORES 8-14 x 3-5 microns from 2-spored basidia, 5-7 x 2-3.5 microns from 4-spored basidia, slightly curved, smooth, colorless; spore print white, (Lincoff), PSEUDOACANTHOHYPHIDIA present and [on the basis of subgenus definition] acuminate-tipped (sharp-tipped) HYPHIDIA, (Chamuris(3))

Notes:
Stereum sanguinolentum has been found in BC, WA, OR, ID, AB, MB, NB, NF, NS, ON, PE, PQ, SK, YT, AK, AZ, CA, CO, CT, MA, ME, MI, MT, NC, NH, NM, NY, PA, TN, UT, VA, VT, WI, and WY, (Ginns). It also occurs in Scandinavia (Eriksson), and in Europe including Switzerland and Asia, (Breitenbach).