Summary:
Features include 1) a perennial fruitbody that is hoof-shaped to flat-projecting or effused-reflexed, 2) cap surface that is brown to blackish, with the rounded margin sometimes yellowish brown, 3) small circular pores that are yellowish brown or grayish brown, 4) growth on oak or other hardwoods, and 5) microscopic characters including ventricose cystidia with elongated slender apices (found also in other members of a Phellinus robustus complex). See comments in the SIMILAR section of Fomitiporia fissuratus which is a competing name for some or all records. The description is derived from Gilbertson(1) except where noted.

Odor:
indistinct (Buczacki)

Taste:
indistinct (Buczacki)

Microscopic:
spores 6-8.5 x 5.5-7 microns, nearly round, smooth, dextrinoid, colorless, thick-walled when mature; basidia 4-spored, 11-12 x 8-9.5 microns, broadly ellipsoid, no clamp connection; cystidia usually abundant in hymenium, ventricose with narrow tapered apex (narrow apical part 1.5-2 microns wide), colorless, thin-walled; setae lacking or occasional in some specimens, 18-37 x 5-8 microns, subulate [awl-shaped] to ventricose, thin-walled to thick-walled; hyphae of context of 2 types: 1) 2.5-4 microns wide, brown in KOH, "thick-walled, rarely branched, rarely simple-septate", 2) inconspicuous, 2.5-5 microns wide, colorless, "thin-walled, simple-septate"; hyphae of trama similar

Spore Deposit:
white (Buczacki)

Notes:
In western North America it is found in BC, and it is also known from CA and NM. Reports on conifers in Alaska and BC may have been based on misidentification (Ginns(28)). It occurs in CA, LA, NM, and TX, (Gilbertson(1)). A competing name for some or all the records of this species in the Pacific Northwest is Fomitiporia fissurata, described in 2016 from California, with supporting material from Arizona, and range extending to New Mexico, (Vlasak(2)).

Synonyms and Alternate Names:
Phellinus robustus (P. Karst.) Bourdot & Galzin