Summary:
Boreostereum radiatum is "readily recognized by its bright, ferruginous hymenium with shallow broad ridges radiating from the center to the margin, and by the black upper side of the pileus when reflexed", (Burt). Features include 1) resupinate growth on wood, with the margin free all round and sometimes bent outward on the upper side to form a shelf-like cap, 2) a leathery fruitbody, with the spore-bearing surface rusty brown, uneven, with radiating thick ridges, 3) a cap when present that becomes black, velvety, crisped, and somewhat lobed, 4) spores that are slightly curved, smooth, and inamyloid, 5) cystidia that are thin-walled and lightly encrusted, 6) a dimitic hyphal system, the septa without clamp connections, and 7) sections staining yellow-green in KOH.

Microscopic:
SPORES 7.5-10 x 3-3.5 microns, inamyloid; CYSTIDIA 2-4 microns wide, thin-walled, lightly encrusted; HYPHAE dimitic, generative hyphae simple-septate, (Martin), SPORES from spore collections 9-10 x 3.5-4 microns, slightly curved, smooth, white; hyphae 3.5-4 microns wide, densely and longitudinally arranged, colored, but color dissolved by dilute KOH; no CYSTIDIA, (Burt), microscopic sections staining yellow-green in KOH, HYPHAE dimitic: generative hyphae simple-septate, and skeletal hyphae yellow, (Ginns(23))

Notes:
Boreostereum radiatum has been found in BC, WA, ID, AB, MB, ON, PQ, AZ, IA, MA, ME, MI, MN, MT, NH, NY, PA, TN, VA, VT, and WI, (Ginns(5)). Collections were examined from ON, MA, MI, MT, NY, PA, VT, and Russia, (Burt).

Synonyms and Alternate Names:
Polyporus delectans Peck