GASTROBOLETUS XEROCOMOIDES Trappe and Thiers, Brittonia 21:247. 1969

Gastrocarp 30-60 mm broad, convex to plano-convex; peridium dry, tomentose, occasionally somewhat rimose, suggestive of Boletus subtomentosus; color olive yellow ("Isabella color" or "tawny-olive" to as dark as "Saccardo's umber"); margin incurved, entire. Context up to 1.5 cm thick at disc, whitish but staining brown in some areas and blue in others when exposed.

Gleba tubulose, the tubes up to 1.5 cm long, not vertically oriented, deep yellow ("old gold"), staining blue where cut or bruised; pores concolorous but staining brownish to ochraceous where bruised.

Stipe-columelia poorly developed, 1-2.5 cm long, 0.4-0.8 cm broad, occasionally much shorter or lacking, equal or tapered downward; surface dry, glabrous to furfuraceous, pallid to pale tan ("warm buff"), staining brown with age or where bruised. Context pallid at apex, grading to distinctly reddish at the base, staining blue in irregular areas when exposed.

Spores 12.8-18(21) X 6.4-8 Ám, smooth, ellipsoid to subcylindric, inequilateral, pyriform, or slightly constricted in the middle, about 50 percent being truncate, yellowish in KOH.

Basidia 30-38 X 10-12 Ám, clavate, yellow in KOH, with one to four sterigmata, hyaline. No hymenial cystidia noted.

Tube trama of parallel to subparallel hyphae 4-8 Ám broad; hyaline to pale yellowish in KOH and light yellow in Melzer's. Peridial trama of interwoven hyphae 3-10 Ám wide; hyaline to pale yellowish in KOH, in Melzer's pale to deep reddish brown to dull yellow. Peridial cuticle a trichodermium of erect hyphal tips with subcylindrical to tapered terminal cells, hyphae 5-10 Ám wide; golden brown in KOH, orange brown to reddish brown in Melzer's; hyphae irregularly incrusted with bands or patches of golden-yellow material that slowly dissolves in KOH or Melzer's. Cuticle of stipe-columella differentiated as a hymenium of fertile basidia. Clamp connections absent.

Habit, habitat, and distribution Gregarious in humus in coniferous forests usually in the vicinity of red fir at higher elevations in the Sierra Nevada in late summer.

Material studied Sierra County: Yuba Pass, Thiers 13163, 21116.

Observations This gastrobolete, showing obvious affinities with the xerocomoid group of boletes, is the only known species with truncate spores. The structure of the apical pore is similar to that in Boletus truncatus. The erratic bluing of the context and the dry tomentose peridium are macroscopic characters similar to species formerly placed in Xerocomus. Microscopically, similarities are seen in the structure of the cutis, including the incrustations on the cuticular hyphae.

Edibility undetermined.

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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