What You Should Know
An easy identify a family of mushrooms, the Rustgills have rusty-looking gills and this one is common and can grow in large numbers on conifer debris or woodchip.
Gymnopilus penetrans is characterized by an orange-brown to the 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.
Common Rustgills grow on rotting stumps, fallen branches, and the forest floor wherever conifer debris has become buried beneath needle litter. Conifer cones, sawdust, or wood chippings seem to be equally acceptable fare for these fiery fungi.
This mushroom is classed as inedible possibly poisonous so is best avoided.
Other names: Common Rustgill.
Gymnopilus penetrans Mushroom Identification
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 a 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 Look-Alikes
Is larger and retains a stem ring; it occurs in woodland habitat, but unlike Gymnopilus penetrans it is seen more often on hardwood stumps and ailing trees, and only occasionally on conifers.
Is a much larger and rarer mushroom with a granular cap and lower stem; its spores are light yellow-brown.
Gymnopilus penetrans Taxonomy and Etymology
The Common Rustgill was described in 1815 by the great Swedish mycologist Elias Magnus Fries, who called it Agaricus penetrans. In 1912 American mycologist William Alphonso Murrill (1869 - 1957) transferred this species to the genus Gymnopilus, thereby establishing its currently-accepted scientific name Gymnopilus penetrans.
Synonyms of Gymnopilus penetrans include Flammula hybrida,Gymnopilus hybridus, Agaricus penetrans Fr., Flammula penetrans (Fr.) Quél., and Dryophila penetrans (Fr.) Quél.
Gymnopilus was proposed as a new genus name in 1879 by the Finnish mycologist Petter Adolf Karsten (1834 - 1917). The origin of this generic name is the prefix Gymn- meaning naked, and the suffix -pilus which means cap - hence naked or bald caps would be an expected feature of the mushrooms in this genus.
The specific epithet penetrans means penetrating.
Gymnopilus penetrans Video
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