Index Fungorum 146: 1. 2014.
Common Name: red stemmed bitter bolete
Synonym: Boletus rubripes Thiers
Cap 6.0-16.0 (20) cm broad, convex, plano-convex at maturity; margin incurved, then decurved, extending beyond the edge of the pore layer; surface dry, buff-brown, matted-tomentose, "chamois-like," darkening with handling, patchy-areolate in dry weather, the cracks revealing a pallid ground color; context 2.0-3.5 cm thick, firm when young, then soft, cream-yellow, rapidly bluing when cut or bruised, sometimes developing pinkish areas; odor mild, sometimes reported as unpleasant; taste slightly bitter
Pores fine, stuffed in youth, approximately 2 per mm at maturity, oval to angular, cream-yellow, becoming dingy ochre-brown, bluing when injured; tubes 1.0-2.0 cm long, colored like the pores, bluing when cut, depressed near the stipe.
Stipe 6.0-15.0 cm long, 3.0-5.0 cm thick, solid, equal, narrowed, or swollen below; surface of apex lemon-yellow, not reticulate, the lower portion striate, reddish, becoming reddish-purple; yellowish mycelium at the base; context firm, white to cream above, vinaceous at the base; partial veil absent.
Spores 12.0-16.5 x 4.5-5.5 µm, smooth, thin-walled, narrowly ellipsoid in face-view, subfusoid and slightly inequilateral in profile; hilar appendage inconspicuous; one to several guttules present; spore print olive-brown
Solitary or in small groups in mixed hardwood/conifer woods, Coast Ranges and at mid-elevations of the Sierra Nevada mountains; fruiting after fall rains, occasionally in the spring; fairly common, especially in wet years.
If appearances equated with edibility, then Caloboletus rubripes would be a culinary favorite. Unfortunately, this attractive bolete is bitter, making it useless for the table. Its size and cap color are suggestive of Boletus edulis and confusion is possible when viewed from a distance. In hand, however, the differences are obvious. While both often have tan-colored caps, the cap surface of Caloboletus rubripes is "chamois-like" rather than glabrous, its pores instantly blue when bruised, and it has a non-reticulate stipe which is yellow at the apex and reddish at the base. Other large boletes that should be compared include Butyriboletus persolidus and its close cousin Butyriboletus autumniregius which have bluing pores but caps that are reddish-brown to rose-pink, Boletus calopus with a tan-brown colored cap, but a reticulate stipe, and Boletus smithii, which has greyish often scarlet-tinged cap, and a stipe that is reddish at the apex, yellowish at the base.
Bessette, A.E., Roody, W.C. & Bessette, A.R. (2000). North American Boletes: A Color Guide to the Fleshy Pored Mushrooms. Syracuse University Press: Syracuse, NY. 400 p.
Desjardin, D.E., Wood, M.G. & Stevens, F.A. (2015). California Mushrooms: The Comprehensive Identification Guide. Timber Press: Portland, OR. 560 p.
Thiers, H.D. (1965). California Boletes. I. Mycologia 57(4): 524-534. (Protologue)
Thiers, H.D. (1975). California Mushrooms—A Field Guide to the Boletes. Hafner Press: New York, NY. 261 p. (WWW)
Vizzini, A. (2014). Nomenclatural novelties. Index Fungorum no. 146: 1-2. PDF