Mycologia 4: 254. 1912.
(sensu Jan Holec in Funga Nordica, 2012; not sensu Hesler in North American Species of Gymnopilus, 1969)
Common Name: none
Cap 4-7 (8) cm broad, at first obtuse-conic, becoming convex, finally plano-convex, with or without a low umbo; margin incurved, at maturity decurved, occasionally wavy; surface appearing glabrous but with innate fibrils and scales when viewed with hand lens; color tawny-brown to rusty brown; margin buff to yellow, with sparse, white veil fibrils in youth; context up to 20 mm thick, soft, cream to buff, unchanging; odor mild; taste bitter.
Gills close, adnexed to notched with a decurrent tooth; in youth, cream, yellowish buff, to buff orange, maturing dull orange, bruising or spotted brown in age; edges even; lamellulae in 3-4 series.
Stipe 30-70 x 5-10 mm in width, cylindrical, more or less equal, central core stuffed; surface cream to pale yellow, inconspicuously pruinose at apex, elsewhere fibrillose-striate, the fibrils becoming tawny to orange brown from spore deposit and where handled; partial veil cortinate, cream to pale yellow, leaving a poorly defined zone high on the stipe and scattered fibrils on lower stipe; dense white mycelium at the base.
Spores 7-8.5 x 4.5-5 microns, ellipsoid, slightly inequilateral in profile, warted at 1000X, dextrinoid in Melzer’s reagent, hilar appendage inconspicuous, germ pore absent, spores rusty brown in deposit; plueurocystidia present but inconspicuous.
Gregarious or in groups on wood chips and conifer logs and stumps, especially those of Monterey pine (Pinus radiata) in the San Francisco Bay Area; fruiting from fall to mid-winter.
Gymnopilus penetrans is characterized by an orange brown to tawny brown cap, the margin pallid to yellowish with sparse whitish veil fibers when young, and a cream to pale yellow fibrillose-striate stipe that becomes rusty brown in areas from spore deposit and handling. We have chosen to follow Holec’s 2012 treatment of Gymnopilus penetrans in Funga Nordica, in part because the species was described from Europe and because Holec’s description matches closely material found in the San Francisco Bay Area. Gymnopilus penetrans is confusable with several California Gymnopilus species. Most similar is Gymnopilus sapineus, at one time considered conspecific with G. penetrans. According to Holec, Gymnopilus sapineus, like G. penetrans can have a tawny colored cap with a paler margin, but the cap is “fibrillose-tomentose to finely scaly”, a character best seen at the disc. Additionally the young gills and stipe are more yellow than in G. penetrans. Another look-alike, Gymnopilus luteocarneus, described by Hesler, is a smaller species, only 3-5 cm broad, the cap rusty-orange and glabrous; it differs in possessing a yellowish veil and microscopically by well-developed pleurocystidia that extend beyond the height of the basidia. Gymnopilus echinulispsorus described by Murrill also mimics G. penetrans, with a rusty orange, glabrous appearing cap, but unlike the latter, it lacks a veil, pleurocystidia, and has spores that are echinulate as the species epithet suggests.
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Hesler, L.R. (1969). North American Species of Gymnopilus. Hafner Publishing Company: New York, NY. 117 p.
Holec, J. (2005). The Genus Gymnopilus (Fungi, Agaricales) in the Czech Republic with Respect to Collections from tther European Countries. Acta Musei Nationalis Pragae, Series B, Historia Naturalis 61(1-2): 1-52.
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Watling, R., Gregory, N.M. & Orton, P.D. (1993). British Fungus Flora: Agarics and Boleti. Vol 7. Cortinariaceae p.p.: Galerina, Gymnopilus, Leucocortinarius, Phaeocollybia, Phaeogalera, Phaeolepiota, Phaeomarasmius, Pleuroflammula, Rozites & Stagnicola. Royal Botanic Garden: Edinburgh, Scotland. 131 p.