BOLETUS CALOPUS var. FRUSTOSUS (Snell and Dick) Miller and Watling, Notes Roy.Botan. Garden, Edinburgh 28:322. 1968
Boletus frustosus Snell and Dick, Mycologia 33:194. 1941.

Pileus 10-20 cm broad, convex when young, becoming broadly convex to plano-convex at maturity; surface dry, dull, tomentose to fibrillose when young, becoming subtomentose and typically areolate or rimose to frustose with age; color brown ("buffy brown" to "snuff brown") when young, changing to dark yellow brown ("Saccardo's umber") to dark brown ("bister") with age, context as seen in the cracks colored pale tan ("pale olive-buff"); margin typically sterile, entire, incurved. Context 2-3 cm thick, pale yellow, quickly changing to blue when exposed, then fading to olive brown ("tawny-olive"). Taste strongly and lingeringly bitter; odor slight or absent.

Tubes 1-2 cm long, adnate when young, becoming deeply and typically narrowly depressed with maturity, pale yellow ("massicot yellow"), becoming darker yellow ("old gold" to "olive lake") with age, changing to blue immediately upon bruising; pores 0.5-1.5 mm broad, angular, concolorous with tubes, bluing when bruised.

Stipe 6-14 cm long, 3-6 cm thick at apex, equal to bulbous, solid; surface dry, reticulate, yellow ("barium yellow" to "massicot yellow"), but typically overlain or partially masked with pink to red discolorations; reticulations sometimes yellow over the reddish background, frequently reddish at apex and yellow below. Context white to yellow, quickly changing to blue when exposed.

Spore print dark olive brown. Spores 14-17 X 4-6 Ám, hyaline to pale yellow in KOH, hyaline in Melzer's, ellipsoid to subfusoid in face view, inequilateral and ventricose in side view, smooth, moderately thick-walled.

Basidia 30-45 X 10-13 Ám, clavate, four-spored, hyaline. Hymenial cystidia 33-48 X 5-10 Ám, scattered, inconspicuous, hyaline, thin-walled, narrowly fusoid-ventricose to cylindric.

Tube trama hyaline, divergent, with conspicuously amyloid septa. Pileus trama interwoven, strongly amyloid, homogeneous, some hyphae with strongly amyloid septa. Pileus cuticle differentiated as a loosely interwoven trichodermium staining ochraceous in KOH with numerous free hyphal tips, often showing incrustations, hyphae 6-10 Ám. wide. Stipe cuticle differentiated as a layer of basidia and cystidia similar to the hymenium.

Chemical reaction KOH-context pale vinaceous; NH4OH-context pale blue; HNO3-context vinaceous, cuticle scarlet; sulfoformalin-cuticle scarlet; FeSO4-context gray.

Habit, habitat, and distribution Solitary to gregarious in soil under conifers, particularly firs, at higher elevations. Often partially buried in the soil. At present this species is known only from higher elevations in the Sierra Nevada and Cascade ranges; however, it probably occurs in all the mountain ranges where red or white firs are established. Boletus calopus is most frequently found in late summer (August-September) following the thunderstorms often prevalent during that time.

Material studied Madera County: Thiers 20875, 20882, 20888, 20913. Mariposa County: Thiers 21052. Mendocino County: Thiers 26904. Nevada County: Thiers 13129, 13156, 13162. Sierra County: Thiers 13204, 13226, 13257, 21186, 23638, 23948, 23949. Siskiyou County: Thiers 23493. Stanislaus County: Thiers 17035. Tuolumne County: Thiers 13274, 17004, 21065, 21113.

Observations This bolete, often massive and heavy, is easily recognized by the dull-brown color of the dry, more or less streaked or fibrillose pileus, which, in dry weather, often becomes severely cracked or areolate, the noticeably bitter taste, and the reticulate stipe, which characteristically shows a combination of red and yellow colors. Microscopically, it is further distinguished by the amyloid reaction of the trama and of the septa or cross walls of the hyphae.

In a recent study Miller and Watling reached the conclusion that typical B. calopus does not occur in this country. Their decision was reached after a critical comparison of European and American collections. Whether this decision will be generally adopted is uncertain since similar comparisons have convinced others that the typical form is in this country, particularly in the Pacific Northwest. The variety included here was first collected in the Mount Shasta area by Cooke. The basidiocarps differ from typical B. calopus by possessing deep, conspicuous fissures in the pileus and were described as new by Snell and Dick under the name of B. frustosus. Miller and Watling, however, decided that these basidiocarps merely represented an extreme areolate or frustose condition of B. calopus, and reduced B. frustosus to varietal status.

This species is not considered poisonous, but is inedible because of the bitter taste.

Online edition addendum

Other Descriptions and Photos: Boletus calopus photo © Michael Wood
Boletus calopus photo © Michael Wood

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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