Summary:
{See also Stereum Table.} Features include 1) resupinate growth on hardwood, or less often with cap-like marginal zones, which may form dense shingled clusters, 2) when present, a cap that is leathery, narrow, wavy or lobed, at first finely tomentose and grayish, soon becoming bald and dark brown, finally black in narrow and sharp zones, 3) a spore-bearing surface that is smooth to uneven or tuberculate, pale ochraceous to buff, bleeding when cut or touched in fresh state, the fluid first reddish, but soon blackish brown, 4) a margin that is white to pale ochraceous and rounded, 5) a distinctly layered appearance in section, each yearly zone defined by a thin dark line, 6) spores that are elliptic, smooth, amyloid, and colorless, 7) pseudoacanthohyphidia, thick-walled cystidia arising from thick-walled skeletal or skeletoid hyphae, and presumably sharp-tipped hyphidia, and 8) hyphae of 2 types a) thin-walled to thick-walled, with frequent branching, septa without clamp connections, and b) thick-walled, sparsely branched, without septa. |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 6.5-9 x 3.5-4.5 microns, elliptic, sometimes flattened on one side, smooth, amyloid, colorless; BASIDIA 4-spored, 25-40 x 5-7 microns, narrowly clavate, without basal clamp connection; PSEUDOACANTHOHYPHIDIA with pointed outgrowths, 25-35 x 3-4 microns; CYSTIDIA none, but ends of conducting hyphae emerging from skeletal hyphae 5-6 microns wide, up to over 250 microns long, cylindric to acuminate, thick-walled, some 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 7-12 x 3-4.5 microns, narrowly elliptic to cylindric, slightly bent, smooth, amyloid, thin-walled; BASIDIA 4-spored, 30-50(100) microns, elongated clavate; CYSTIDIA of 2 types: 1) pseudoacanthohyphidia easily observed, 30-35 x 3-4 microns, projecting slightly beyond the basidia, 2) pseudocystidia 5-12 microns wide, usually more than 100 microns long, "thick-walled, except for the apical part, slightly projecting, smooth, more or less constricted", colorless to yellowish, with oily content; HYPHAE monomitic with simple-septate hyphae of 2 types, "hymenial hyphae thin-walled, 3-4 microns wide, branching frequent, tramal hyphae thick-walled, horizontal, 3-6 microns wide, hyphae in the tomentum are of an intermediate type, sparingly branched, hyaline to yellowish and in cortex pale brown and fairly thick-walled", (Eriksson), SPORES 7-12 x 3-6 microns, PSEUDOACANTHOHYPHIDIA present and [on the basis of subgenus definition] acuminate-tipped (sharp-tipped) HYPHIDIA, (Chamuris)

Notes:
Stereum rugosum has been found in BC, ID, NB, NF, NS, ON, PE, PQ, AK, MI, MN, NC, NH, NY, PA, and TN, (Ginns). It is common in Scandinavia (Eriksson), and occurs also in Switzerland and Asia, (Breitenbach).

Synonyms and Alternate Names:
Haematostereum rugosum (Pers.) Pouzar