Summary:
The most conspicuous features are the radially elongated, relatively thick-walled pores and the pronounced umbo that typically develops at the base. Other features include a relatively large, bracket-like, approximately semicircular fruitbody with a tough texture, a bumpy-wavy surface that is whitish to ocher or green from algae, a whitish to gray-ocher pore surface, and microscopic characters including elliptic-cylindric spores and a trimitic hyphal system. Domanski(1) described five forms from Eurasia. Forma gibbosa has dimidiate fruitbodies 1-4cm thick, with the white to yellowish upper surface velvety, chamois-like or tomentose (usually bald when old), and pores "more or less rectangular or elongated, radially arranged, sometimes labyrinthine". Forma tenuis has a thinner fruitbody with tubes often confluent and merging into almost gill-like structures. Forma hirsuta is "of moderate size, with a thin margin and zonate surface, covered with dense gray hairs" (resembling those of Trametes hirsuta). Forma kalchbrenneri has a velvety to almost bald surface, zonate with belts either throughout or near the margin, and grayish-ochraceous, light- or rufous-cinnamon in color. Forma amurensis (east Asia) has an azonate or weakly zonate upper surface that is white (cream to grayish when dry), tubes 0.5-1cm long, with thinner walls than forma gibbosa and smaller (0.5 millimeters diameter), circular or angular, radially arranged pores.

Odor:
like Heterobasidion annosum [which the authors describe as "strongly fungoid"], (Breitenbach)

Taste:
somewhat bitter (Breitenbach)

Microscopic:
spores 4-5.5 x 2-2.5 microns, elliptic-cylindric, smooth, inamyloid, colorless, sometimes with droplets; basidia 4-spored, 15-22 x 5-8 microns, clavate, with basal clamp connection; cystidia not seen; hyphal system trimitic, generative hyphae 2.5-4.5 microns wide, septa with clamp connections, skeletal hyphae 5-6 microns wide, thick-walled, binding hyphae 2-3 microns wide, branched, thick-walled, (Breitenbach), spores 4-5 x 2-2.5 microns, cylindric to oblong-elliptic and often slightly bent, smooth, inamyloid, colorless, thin-walled; hyphal system trimitic: generative hyphae 2-4 microns wide, colorless, thin-walled, with clamp connections, skeletal hyphae "dominating in the fruitbody", 3-6 microns wide, thick-walled to almost solid, binding hyphae 2-5 microns wide, "mostly restricted to the trama, scarce and scattered in the context, tortuous and strongly branched, more rarely with long unbranched segments", (Ryvarden(2)), basidia 14-18 x 3-5 microns; cystidia absent, fusoid cystidioles present, 13-19 x 4-5 microns; generative hyphae 2-4 microns wide, branched, colorless, thin-walled, with clamp connections, skeletal hyphae 4-9 microns wide, thick-walled to subsolid, colorless, nonseptate, binding hyphae 2-4 microns wide, tortuous, thick-walled to solid, colorless, intermediate forms exist between binding and skeletal hyphae, (Ryvarden(3))

Spore Deposit:
white (Buczacki)

Notes:
Distribution includes BC, WA, and OR (Ginns), WI (Neuman), QC, PA, southeastern United States, (Kout), Denmark, Norway, Sweden, United Kingdom to USSR where beech grows, (Ryvarden(2)), Europe, China, Siberia, (Domanski), and Japan (Ryvarden(3)).

EDIBILITY

not edible (Phillips(2))

Synonyms and Alternate Names:
Clavaria stricta Pers.
Daedalea gibbosa Pers.
Lenzites gibbosa (Pers.) Hemmi
Pseudotrametes gibbosa (Pers.) Bondartsev & Singer