Pileus 5-8 cm broad at maturity, broadly convex when young, becoming plane with slightly elevated or uplifted margin when older; surface dry, dull, velutinous to subtomentose, typically becoming noticeably areolate with age; color brown to dark brown ("Prout's brown" to "cinnamon-brown") to sometimes as pale as buff ("warm buff"), occasionally with rust-colored tinges or flushes when older; margin entire, decurved, becoming plane or uplifted. Context up to 1 cm thick, yellow ("Martius yellow"), changing to blue immediately upon exposure. Taste and odor mild.
Tubes 1 cm in length, decurrent to adnate, greenish yellow ("light greenish yellow") when young, becoming olive yellow ("olive lake" to "sulphin yellow") when older, bluing immediately when bruised; pores 1 mm broad, angular, yellow, bluing quickly when bruised.
Stipe 4-7 cm long, 1-2.5 cm thick at the apex, equal or tapering toward the base, stuffed; surface dry, obscurely punctate or furfuraceous, sometimes longitudinally ridged, not reticulate, bright yellow ("Martius yellow") at the apex, changing to deep yellow ("antimony yellow") in midportion and typically reddish brown ("russet" to "Mars brown") toward the base, bluing when handled. Context yellow, turning blue immediately upon exposure.
Spore print dark olive to olive brown. Spores 14.0-17.5 X 4-6.5 Ám ochraceous in KOH, weakly amyloid, subellipsoid to subfusoid in face view, ventricose in side view, many appearing obscurely truncate with no annular thickening and no germ pore, smooth, moderately thick walled.
Basidia 25-32 X 6-9 Ám, four-spored, clavate, hyaline. Hymenial cystidia 45-60 X 10-16 Ám, scattered to rare, hyaline, thin-walled, fusoid to clavate, often with elongated tapering apices.
Tube trama obscurely divergent from mediostratum, which stains brown in KOH, hyphae 3-5 Ám wide. Pileus trama homogeneous, interwoven. Pileus cuticle differentiated as a tangled trichodermium staining dark brown in KOH, with numerous free, erect hyphal tips. Stipe cuticle not differentiated. Clamp connections absent.
Chemical reactions According to Singer, the following reactions occur: KOH-cuticle darkening; HNO3-cuticle red.
Habit, habitat, and distribution Solitary in humus in mixed coastal forest. Known only from a single collection made in the vicinity of Eureka. It is apparently more abundant in Washington, Oregon, and Idaho, where several collections have been made.
Material studied Trinity County: Lamphere 12-6-62.
Observations The inclusion of this species is based upon a collection consisting of only a single fruit body. Had it not been for an abundance of material from the adjacent northwestern states, it would have been omitted. It is distinguished by the dull, dark-brown, tomentose pileus, which in the western United States characteristically becomes rimose-areolate with age, and by the immediate change to blue of all parts of the basidiocarp when bruised or exposed. As indicated, some spores are frequently obscurely truncate, and it is interesting to speculate as to the significance of this feature from a phylogenetic point of view. In view of the recent discovery of at least three species having distinctly truncate spores, it is quite possible that B. pulverulentus represents an intermediate stage.
Edible, but so rare as to be of no significance.
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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