BOLETUS CHRYSENTERON Saint-Amans, Flore Agenaise, p. 555. 1821
Xerocomus chrysenteron (Saint-Amans) Quelet, Fl. Mycol. Fr., p. 418. 1888.
Ceriomyces communis (Secretan, pro parte) Murrill, Mycologia 1:155. 1909.
Illustrations: See Microfiche No. 5
Kawamura, S., Icones of Japanese Fungi, pl. 235.
Lange, J. E., and M. Lange, 600 Pilze in Farben, p. 189.
Leclair, A., and H. Essette, Les Bolets, pl. 21.
Romagnesi, H., Nouvel Atlas des Champignons, pl. 123.
Singer, R., Die Rohrlinge, Teil 1, pl. XII, figs. 5-12.
Smith, A. H., The Mushroom Hunter's Field Guide, p. 105.
Smith, A. H., and H. D. Thiers, The Boletes of Michigan, pl. 105.
Snell, W. H., and E. A. Dick, The Boleti of Northeastern North America, pl. 123.

Pileus 6-8 cm broad when expanded, convex changing to broadly convex to plano-convex to plane at maturity; surface dry, dull, velutinous to tomentose, usually shallowly and conspicuously areolate with age, especially near the margin; color dark brown ("Saccardo's umber" to "snuff brown") to occasionally blackish brown ("sepia" to "bister") during all stages of development; context in cracks on disc pallid, usually assuming reddish tints toward the margin when older; margin entire, decurved. Context 1-1.5 cm thick, yellow ("ivory yellow" to "light buff" to "pale chalcedony yellow"), unchanging or becoming blue in irregular areas when exposed. Taste not distinctive to somewhat acid and unpleasant; odor not distinctive.

Tubes 1 cm in length, arcuate-decurrent to depressed, often narrowly and deeply so in older carpophores, colored yellow ("reed yellow" to "old gold"), typically changing to blue when bruised; pores large (1-1.5 mm broad), typically highly irregular in outline, concolorous with the tubes.

Stipe 7-10 cm long, 1-1.7 cm thick at the apex, equal to tapering slightly toward the base, solid, whitish to yellow mycelium at the base; surface dry, glabrous but often longitudinally ridged or striate, usually yellow ("primrose yellow") at the apex becoming reddish ("russet" to "tawny" to "Hay's russet") toward the base, sometimes pallid at the base and reddish only in midportion, or entirely pallid with only the striations or ridges colored red ("Eugenia red"). Context pallid to yellowish at the apex, typically changing to reddish toward the base, unchanging when exposed.

Spore print olive brown. Spores 12-13.5 X 5-6 Ám, ochraceous in KOH and Melzer's reagent, ellipsoid to subventricose to subcylindric, not truncate, smooth.

Basidia 33-36 X 7-9 Ám, hyaline, four-spored, clavate. Hymenial cystidia 56-75 X 10-13 Ám, scattered to numerous, common only on the pores, fusoid to fusoid-ventricose, hyaline, thin-walled.

Tube trama hyaline, obscurely divergent to subparallel, hyphae ▒8 Ám wide. Pileus trama homogeneous, interwoven, hyaline, hyphae ▒7 Ám wide. Pileus cuticle staining dark cinnamon brown in KOH, a trichodermium with slightly differentiated hyphal tips, hyphae ▒10 Ám wide, often heavily and spirally incrusted. Stipe cuticle interwoven, incrusted, staining dark cinnamon brown in KOH. Clamp connections absent.

Chemical reactions KOH-context negative to pinkish yellow, cuticle negative or darkening slightly; HCl-context negative to yellowish, cuticle negative to pinkish; HNO3-context and cuticle negative to pale pink; sulfoformalin-context and cuticle negative to pale pink.

Habit, habitat and distribution Solitary to gregarious in soil in mixed forests. This bolete has been found in many different areas within the state, and probably occurs throughout the forested areas, including those of southern California. Apparently it forms mycorrhizal associations with a broad spectrum of hosts, since it has been found in both coniferous and broad-leaved forests. It is likely to be found more or less continuously, but never abundantly, from early in the fall season through February.

Material studied Butte County: Kowalski 1247. Del Norte County: Thiers 14108, 17639, 17745, 23037. El Dorado County: Thiers 20762, 20809. Humboldt County: Thiers 13748, 14544, 17615, 21385, 22909. Madera County: Thiers 20874, 20938, 23615. Marin County: Madden 694; Ripley 1003. Mendocino County: Largent 65; Theobald 11-2-63; Thiers 8746, 9294, 9470, 9617, 21524, 23065, 24166, 24440. San Diego County: Thiers 25195. San Mateo County: Thiers 9452. Santa Cruz County: Thiers 26970. Sierra County: Thiers 13850, 21182, 23636. Sonoma County: Sundberg 212. Stanislaus County: Thiers 12950, 16983. Tuolumne County: Thiers 21064.

Observations Boletus chrysenteron is a member of a rather difficult complex of boletes. It is distinguished by the dark-gray to grayish-black color of the dry, tomentose to velutinous pileus, the areolate condition of the mature pilei in which reddish pigments develop in the cracks, the yellowish to pallid stipe, which characteristically develops reddish areas with age, and the nontruncate spores. It is most likely to be confused with B. truncatus, from which it can be distinguished most readily by the absence of the characteristic truncate spores, and with B. zelleri, which usually has a noticeably pruinose but not strongly areolate pileus that is very dark colored, almost black, and a cuticle that, at least when young, is composed of a layer of somewhat inflated hyphal tips, which are not usually spirally incrusted. All three of these species often occur in the same area and are frequently quite difficult to separate.

Among other members of this complex are such common species as B. subtomentosus, which is usually more olive to olive brown in color with no red in the cracks, and B. spadiceus, which characteristically shows the blue to blue-green discoloration when ammonium hydroxide is applied to the cap. Boletus amyloideus and Tylopilus amylosporus can all be distinguished by their amyloid spores.

Edible but not choice, and rarely collected for the table. The possibility of confusing its identity with other, possibly untested, species should always be kept in mind.

Online edition addendum

Other Descriptions and Photos: The Fungi of California

The Boletes of California
Copyright © 1975 by Dr. Harry D. Thiers
Additional content for the online edition © 1998 by Michael Wood, Fred Stevens, & Michael Boom
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