BOLETUS ZELLERI Murrill, Mycologia 4:217. 1912
Ceriomyces zelleri Murrill, Mycologia 4:99. 1912.
Xerocomus zelleri (Murrill) Snell ex Slipp and Snell, Lloydia 7:43. 1944.
Boletellus zelleri (Murrill) Singer, Snell, and Dick, Mycologia 51:575. 1959.
Illustrations: See Microfiche No. 23
Smith, A. H., Mushrooms in Their Natural Habitats, Reel 6.
Smith, A. H., The Mushroom Hunter's Field Guide, p. 104.

Pileus 5-10 cm broad at maturity, convex to obtusely convex when young, becoming plano-convex to convex to plane with age; surface dry, conspicuously white-pruinose when young, becoming glabrous to obscurely tomentose to subtomentose with age, rugulose to verrucose when young, becoming more or less even or smooth at maturity, not conspicuously areolate when young, but sometimes becoming so with age; color black to blackish brown ("dusky brown" to "fuscous" to "fuscous-black" to "bone brown"), sometimes fading to dark brown ("army brown" to "Natal brown") often with a reddish margin; margin entire, becoming eroded with age, incurved when young, becoming decurved at maturity. Context up to 1.5 cm thick, whitish to pale yellow, unchanging or becoming blue when exposed. Taste not distinctive or mildly acid; odor not distinctive.

Tubes up to 1.5 cm in length, arcuate-decurrent to depressed, often deeply depressed with age, olive yellow ("olive-ocher") when young, changing to dark yellow ("honey yellow") with age, becoming blue when bruised or exposed; pores typically more than 1 mm broad, highly irregular in outline, concolorous with the tubes.

Stipe 5-8 cm long, 0.7-1.3 cm thick at the apex, equal to occasionally tapering slightly toward the apex, solid, with white to pale-yellow mycelium at the base; surface dry, granulose to punctate, especially toward the base, color tan ("warm buff") when young, becoming more or less obscured with red ("Eugenia red") granules, sometimes red ("acajou red") at the apex, becoming yellowish with red punctae toward the base, old stipes often red ("Vandyke red" to "madder brown"). Context yellow when young, typically red when older, sometimes changing to blue in irregular areas when exposed.

Spore print olive brown. Spores 12-15 X 4-5.5 Ám, occasional giant spore measuring up to 24 Ám in length, pale yellow to pale ochraceous in KOH, ochraceous tawny in Melzer's, subellipsoid to subventricose, smooth.

Basidia 18-21 X 10-11 Ám, hyaline, clavate, four-spored, rarely one- to three-spored. Hymenial cystidia 40-85 X 10-13 Ám, rare to scattered to numerous, apparently lacking in some carpophores, clavate to obtusely fusoid to fusoid-ventricose to obscurely mucronate, hyaline to rarely yellowish in KOH, thin-walled.

Tube trama parallel to obscurely divergent, with a distinct central strand, hyaline, hyphae ▒6 Ám wide. Pileus trama loosely interwoven, homogeneous, hyphae ▒3 Ám wide. Pileus cuticle staining dark brown in KOH, differentiated as a trichodermium of free, septate, erect, inflated hyphal tips, often appearing similar to pileocystidia, incrusted, typically collapsing and appearing as a tangled mass of hyphal tips in older pilei. Stipe cuticle interwoven, heavily incrusted, with laticiferous hyphae differentiated throughout. Clamp connections absent.

Chemical reactions NH4OH--context greenish; HCl-context yellowish, cuticle dark pink; HNO3-context and cuticle pink; sulfoformalin-context yellowish, cuticle dark pink.

Habit, habitat, and distribution Solitary to scattered in humus or soil in the coastal forests and in the Sierra and Cascade mountain ranges. Found most commonly in mixed coastal forests, especially where redwoods are relatively abundant. In some instances it has also been collected along the margin of slash burns and in restricted clearings within the forests. This is a common bolete in California and often fruits from the onset of the rainy period in the fall through March or April.

Material studied Butte County: Ripley 1638. Calaveras County: Sundberg 772. Del Norte County: Thiers 17640. Fresno County: Thiers 13367. Humboldt County: Sundberg 325; Thiers 14106, 14192, 17748, 19265. Marin County: Kady 11-23-68; Madden 677; Shervanick 382; Thiers 9825, 18148. Mendocino County: Ammirati 12-6-64; Motta 51; Peters 90; Thiers 8165, 8202, 8435, 8619, 8870, 8993, 9256, 9289, 9342, 9349, 9854, 10051, 10706, 11076, 12233, 14614, 18104, 24155, 24213. Nevada County: Thiers 13159. San Mateo County: Sund erg 196; Thiers 7449, 11199. Santa Cruz County: Peters 349; Thiers 9088. Shasta County: Thiers 21661. Sierra County: Sundberg 308; Thiers 13209. Sonoma County: Largent 324. Tuolumne County: Thiers 13275.

Observations This fungus appears to be very closely related to B. chrysenteron, and microscopic examination of the cuticle is often necessary to distinguish them. Generally, B. zelleri has a darker-colored pruinose pileus that typically does not become strongly rimose-areolate. It has been found, however, that by far the most reliable distinction is in the difference in the structure of the cuticle of the two species. In young pilei of B. zelleri the cuticle is differentiated as a closely packed trichodermium of noticeably enlarged erect hyphal tips in which the subterminal cell is globose to pyriform and the terminal cell is somewhat pyramidal in outline. In older pilei these cells sometimes collapse and the cuticle then appears repent to interwoven. In B. chrysenteron, on the other hand, the terminal hyphal cells are more or less equal in size and the hyphae are interwoven or more or less radially arranged. Another conspicuous feature of the cuticle of B. chrysenteron is the heavy incrustation on the hyphal walls, which is often deposited in a spiral pattern. The walls of the cuticular hyphae of B. zelleri are often incrusted, but not in a spiral fashion.

Singer, Snell, and Dick transferred B. zelleri to Boletellus chiefly because of their observation that the spores have slightly roughened walls. Careful attention, including the examination of the spores of local collections under oil with phase attachments as well as under oil with apochromatic objectives, failed to reveal any definite roughness or wrinkling of the spore wall. It is possible that their collections were from a different area, thereby representing a different race, or that the roughness has been overlooked in the local collections. It seems preferable to retain the species in Boletus and, if necessary, emend the concept to accommodate occasionally roughened spores.

Edible and generally considered excellent.

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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