Originally described by Berkeley as Fomes fomentarius var. excavatus (Ann. Nat. Hist. 3 : 387. 1839). “The type specimens at Kew agree in all respects with P. fomentarius as it grows in the Adirondack Mountains…” (Murrill, 1903)
139. Fomes excavatus Berk. Ann. N. Hist. 1839, p. 387.
Pileo duro, ungulato, intus cinnamomeo; hymenio excavato, margine obtuso,- poris tenuibus perfecto rotundis, cervinis, intus cinnamomeis.
Pileus 3-4 cm. lat. et long., sordide albus brunneo-zonatus, zonis vix depresses, glaberrimis. In speciminibus annosis adsunt costae 4-5, glabrae, plano-convexae, atro-brunneœ. (Saccardo, 1888)
Pileus hard, ungulate. Hymenium hollowed out. Pileus 1 1/2 inch (3.81 cm) across, 1 1/2 high, dirty white, banded with brown; bands scarcely at all depressed, quite smooth, nearly even. Margin rather obtuse. Pores small, perfectly round, fawn-coloured, cinnamon within. Old specimens have four or five smooth, even, convex, black-brown ridges. Substance cinnamon colored. On birch. Isle a la Crosse. Dr. Richardson.
Habitat/range: On live and dead hardwoods, especially Betula, causing a white mottled rot. Scattered in the southern half of BC, with one northern collection at Fort Nelson. Widespread elsewhere in western North America.
Basidiomata perennial, hard, woody, typically several on a dead tree trunk; pileus 3–15 cm wide × 6–20 cm long × 2–15 cm thick, resembling a horse’s hoof; pileus surface a hard crust ±1 mm thick, glabrous, smooth, not cracked, varying shades of grey; margin brown in growing basidiomata; context brown, darkening in koh but soon fading to brown, soft-corky or punky, 2–25 mm thick; tubes stratified, each layer up to 6 mm deep; pore surface brown; pores round, 3–5 per millimetre, edges thick.
Hyphal system trimitic. Generative hyphae 2–4 μm diameter with clamp connections, walls thin, hyaline, some at the pore surface with walls moderately thick, encrusted; skeletal hyphae 3–8 μm diameter, walls thick, brown; binding hyphae 1.5–3.0 μm diameter, walls hyaline to brown; sclerids (contorted cells in the core) ~ 30–70 × 10–30 μm, walls thick, brown; cystidia lacking; cystidioles fusoid, 24–37 × 3.5–7.5 μm; basidia clavate or urniform, 23–25 × 7–9 μm, four sterigmate; basidiospores narrowly ellipsoid, 12–20 × 4–7 μm, walls hyaline, thin, smooth, neither amyloid nor dextrinoid.
Herbarium location: http://sweetgum.nybg.org/vh/specimen.php?irn=873182
Lowe, J.L., (1955) “Perennial polypores of North America: III. Fomes with context white to rose.” Mycologia 47.2: 213-224.
Murrill, W. A. (1903). The Polyporaceae of North America.-IV. The genus Elfvingia. Bulletin of the Torrey Botanical Club, 296-301.
Saccardo, P.A., (1888) Sylloge Fungorum 6, 180. http://www.cybertruffle.org.uk/cyberliber/02698/0180.htm
Taylor, J.E., et al., (1839) Annals of Natural History, Or Magazine of Zoology, Botany, and Geology, Volume 3 https://books.google.com/...