Summary:
Hyphoderma setigerum is recognized by 1) its characteristic cystidia that are long cylindric, multiply septate with clamp connections, somewhat thick-walled, and often encrusted with crystals. Other features include 2) resupinate growth on hardwood, less often on conifer wood, 3) a membranaceous to waxy, whitish fruitbody with a surface that is smooth to granular, bumpy, or toothed, 4) spores that are cylindric, smooth, inamyloid, and colorless, 5) a monomitic hyphal system, the hyphae with clamp connections. Eriksson(3) comment "Even if it is as a rule easily recognized thanks to its characteristic cystidia, it must be looked upon as a form complex rather than a natural species taxon".

Microscopic:
SPORES 9-10 x 4-4.5 microns, cylindric to cylindric-elliptic, smooth, inamyloid, colorless; BASIDIA 4-spored, 40-45 x 5-6 microns, cylindric-clavate, with basal clamp connection; SEPTOCYSTIDIA up to 220 x 10 microns, cylindric, thick-walled, multiply septate with clamp connections, some encrusted with crystals; HYPHAE monomitic 2.5-4 microns wide, septa with clamp connections, (Breitenbach), SPORES 7-10(13) x 3-4.5(6) microns, narrowly elliptic to suballantoid, "adaxial side often but not always convex", smooth, inamyloid, thin-walled, containing oil droplets; BASIDIA 25-30 x 6-7 microns, subclavate to clavate, with basal clamp connection, normally 4-spored; CYSTIDIA mostly numerous, thick-walled except in the growing apical cell, regularly septate with clamp connections, "at first naked, then encrusted with double-pyramidic crystals", 70-200 microns long and with the clamp connections 10-15 microns wide, "when much encrusted even more", also in some specimens in the subhymenial part there are enclosed, pyriform or bladder-like cells, which appear to be precursors of cystidia; HYPHAE monomitic 3-4 microns wide, thin-walled to somewhat thick-walled, in the subhymenium densely branched, closely united, and predominantly vertical, in the subiculum (which is several millimeters thick in many fruitbodies, especially in the orbicular ones on bark) more horizontal, sparsely branched, loosely interwoven; in hydnoid specimens there is a portion of vertical subicular hyphae in the center of the teeth, (Eriksson), SPORES 9-14 x 4-5 microns, cylindric to slightly allantoid, with small lateral apiculus, inamyloid, acyanophilic, thin-walled; BASIDIA 4-spored, 15-35 x 6-8 microns, clavate, with basal clamp connection, sterigmata about 5-6 x 1.5 microns; CYSTIDIA 100-200 x 7-10 microns, projecting about 30-130 microns, long-cylindric, colorless to slightly yellowish, "mostly septate, smooth or loosely covered with crystals, somewhat thick-walled (up to 1.0 micron)", the primary septa have a clamp connection but the secondary septa of the older cystidia do not; HYPHAE 3-5 microns wide, loosely interwoven, colorless, "thin-walled to somewhat thick-walled (up to 1.0 micron)", with clamp connections, "in older hyphae some secondary hyphae with simple septa present", (Julich)

Notes:
Hyphoderma setigerum has been found in BC, WA, ID, MB, NB, NF, NS, ON, PE, AK, AZ, CA, CO, FL, GA, IA, IL, LA, MD, MI, MN, MS, MT, NC, NM, NY, TN, VA, and WI, (Ginns), in all parts of north Europe, including specifically Finland, (Eriksson), and in Austria, Germany, United Kingdom, (Julich).