BOLETUS TRUNCATUS (Singer, Snell, and Dick) Pouzar, Ceská Mycol. 20:2. 1966

Xerocomus truncatus Singer, Snell, and Dick in Snell, Singer, and Dick, Mycologia 51:573. 1959.

Illustrations: See Microfiche No. 22

Singer, R., Die Rohrlinge, Teil 1, pl. XII, figs. 1-4.

Smith, A. H., and H. D. Thiers, The Boletes of Michigan, pl. 113.

Snell, W. H., and E. A. Dick, The Boleti of Northeastern North America, pl. 26.

Pileus 5-12 cm broad when mature, convex when young, becoming broadly convex to plano-convex to plane at maturity; surface dry, conspicuously tomentose during all stages of development, relatively smooth and even when young, usually becoming strongly areolate with age; color near brown ("tawny-olive" to "buffy brown") when young, darkening to dark brown ("clove brown" to "olive-brown" to "sepia" to "bister") when older, exposed flesh in cracks rarely showing reddish tints; margin entire, incurved. Context 1-1.5 cm thick, tan ("warm buff" to "light buff"), unchanging or becoming blue in irregular areas when exposed. Taste often acid and somewhat unpleasant; odor not distinctive.

Tubes 1-1.5 cm long, subdecurrent to deeply and narrowly depressed around the stipe, greenish yellow ("olive-ocher" to "Isabella color" to "old gold"), bluing readily when bruised; pores more or less 1 mm broad, angular, concolorous with tubes.

Stipe 8-12 cm long, 1.5-3 cm thick at the apex, equal to tapering slightly toward the base, solid, with bright-yellow mycelium at the base; surface dry, glabrous to obscurely punctate or ridged, color red ("hydrangea red" to "dark vinaceous") at the apex, becoming pallid ("warm buff" to "light buff" to "naphthalene yellow") toward the base, usually with red lines or ridges ("Eugenia red"). Context reddish toward the base, pallid at the apex.

Spore print olive brown. Spores 12.5-15 X 4.5-6.0 µm tawny to cinnamon in KOH and Melzer's, ellipsoid to subventricose, conspicuously truncate, with thickened walls surrounding a thin depression in truncate apex, walls smooth.

Basidia 28-33 X 7-10 µm, hyaline, clavate, four-spored. Hymenial cystidia 36-67 X 10-14 µm, scattered to numerous, staining tawny to ochraceous in KOH, incrusted or filled with amorphous content, clavate to elongated fusoid-ventricose.

Tube trama hyaline, obscurely divergent to subparallel, hyphae 6 µm wide. Pileus trama loosely interwoven, hyaline, homogeneous, hyphae 7 µm wide. Pileus cuticle differentiated as a trichodermium of interwoven to more or less radially arranged hyphal tips, often incrusted, staining ochraceous to tawny in KOH, hyphae 10 µm wide. Stipe cuticle differentiated as a layer of caulobasidia with numerous sterile hyphal tips interspersed, staining cinnamon to tawny in KOH, tawny laticiferous hyphae scattered throughout. Clamp connections absent.

Chemical reactions HCl-context yellowish; sulfoformalin-context pink.

Habit, habitat, and distribution Solitary to scattered in humus in mixed forests. It is commonly found along the coast and has been collected from Santa Barbara to the Oregon border. Only one collection has been made elsewhere in California and that was in the vicinity of Paradise in Butte County. It is widely distributed throughout most of the forested regions of the United States. On the west coast it typically fruits during the fall and winter rainy season.

Material studied Butte County: Ripley 1638. Del Norte County: Thiers 17638. Humboldt County: Thiers 14439, 23014; Wennekens 154; White 211. Marin County: Madden 815; Thiers 11134, 18119. Mendocino County: Ammirati 12-6-64; Shamiyeh 11-2-63; Thiers 8203, 14617, 24443. San Francisco County: Thiers 24721. San Mateo County: Motta 12-6-60;Thiers 11917, 18061, 18195, 18355, 21847, 26931, 26991, 27017. Santa Barbara County: Thiers 11797. Santa Cruz County: Thiers 10786, 12038, 17935, 17961, 18532, 26969. Sonoma County: Thiers 9412.

Observations When first seen, this bolete is likely to be determined as B. chrysenteron since they are similar in color and, in both, the pileus typically becomes areolate with age. Boletus truncatus, however, does not usually show the characteristic red or reddish pigment in the cracks as does B. chrysenteron. It should be emphasized that a microscopic examination is necessary, however, before a positive determination of B. truncatus can be reliably accomplished. The noticeably truncate apex of at least a majority of the spores is its major distinguishing characteristic. Macroscopically, B. truncatus is sometimes confused with B. zelleri, which, however, has a distinct pruinose covering on the pileus and is usually darker in color. The cells of the terminal hyphae of the cuticle of B. zelleri are more inflated and the spores are not truncate.

Edibility not determined.