California Fungi—Xerocomellus mendocinensis
Xerocomellus mendocinensis (Thiers) N. Siegel, C.F. Schwarz & J.L. Frank
Fungal Systematics and Evolution 6: 282. 2020.
Common Name: none
Misapplied names: Boletus truncatus (Singer, Snell, & Dick) Pouzar; Xerocomus truncatus Singer, Snell, & Dick; Xerocomellus truncatus (Singer, Snell & E.A. Dick) Klofac
Cap 5-10 cm broad, convex, broadly convex to nearly plane in age; surface dry, tomentose, brown to olive-brown, usually cracking early in development revealing underlying yellowish to pinkish tissue, the latter more prevalent toward the margin; flesh thick, light yellow, typically blueing strongly when injured; odor mild, taste acidic.
Pores +/- 1 per mm, dull yellow to yellowish-green, bruising rapidly blue; tubes up to 1.5 cm long, narrowly depressed near stipe, yellowish-green, quickly and strongly bruising blue.
Stipe 5-10 cm long, 1.5-2.5 cm thick, solid, equal, or the base slightly narrowed; surface dry, smooth to slightly striate, yellowish at the apex, otherwise reddish; yellowish-green mycelium at base.
Spores 12-15 x 4.5-6 µm, smooth, elliptical to fusiform, truncate at one end; spore print olive-brown.
Solitary to in small groups in hardwood/conifer woods from fall to mid-winter.
Edible and good.
This nondescript bolete is closely related to and often confused with Xerocomellus diffractus. Both have an olive-brown to brown tomentose cap typically areolate at maturity, similarly colored stipe, and yellowish mycelium at the base. Xerocomellus mendocinensis, however, is less likely than X. diffractus to develop pinkish tones in cracks near the cap margin, and in our experience the pores bruise blue almost instantly, while in X. diffractus, this reaction takes several seconds with the blueing never as intense. Nonetheless, a microscope is required to make a positive identification. Xerocomellus mendocinensis spores are, as the species name suggests, blunt or clipped at one end, those of X. diffractus, rounded.
Until recent work by Frank et al., this species was known as Xerocomellus truncatus, a morphologically similar, but genetically distinct Eastern United States species that is not known to occur in the west.
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Desjardin, D.E., Wood, M.G. & Stevens, F.A. (2015). California Mushrooms: The Comprehensive Identification Guide. Timber Press: Portland, OR. 560 p.
Frank, J., Siegel, N., Schwarz, C., Araki, B. & Vellinga, E. (2020). Xerocomellus (Boletaceae) in western North America. Fungal Systematics and Evolution 6: 265-288. (PDF)
Klofac, W. (2011). Rotfußröhrlinge (Gattung Xerocomellus) in aktueller Sicht. Österreichische Zeitschrift für Pilzkunde 20: 35-43.
Ladurner, H. & Simonini, G. (2003). Xerocomus s.l. Edizioni Candusso: Alassio. 527 p.
Siegel, N. & Schwarz, C. (2016). Mushrooms of the Redwood Coast. Ten Speed Press: Berkeley, CA. 601 p.
Smith, A.H. & Thiers, H.D. (1971). The Boletes of Michigan. University of Michigan Press: Ann Arbor, MI. 426 p.
Snell, W.H., Singer, R. & Dick, E.A. (1959). Notes on Boletes. XI. Mycologia 51(4): 564-577. (Protologue)
Thiers, H.D. (1975). California Mushrooms—A Field Guide to the Boletes. Hafner Press: New York, NY. 261 p. (WWW)
— rarely the pores can have a reddish cast
