This is a gorgeous and impressive mushroom, found under spruces at high elevations in the Rocky Mountains in late summer and early fall. It is a member of the North American Boletus edulis group, and I think it is closer to the "true" Boletus edulis of Europe than most of its North American counterparts--or, more precisely, it seems virtually identical to the reddish-capped version of Boletus edulis I have collected many times under Scots pine (Pinus sylvestris) in Finland, which European mycologists usually call "Boletus pinophilus"--though they often concede it "may indeed be nothing more than a variety of B. edulis" (Breitenbach & Kränzlin, 1991).
The reddish to reddish brown, greasy-when-fresh cap surface is distinctive, as is the large stature. Fist-sized buttons can often be found barely emerging from the duff--and at maturity the cap can be nearly as wide as a dinner plate. Amanita muscaria is often fruiting nearby, as well as Sarcodon imbricatus.
An apparently undescribed Boletus species growing under pines along the Gulf Coast is sometimes called "Boletus pinophilus," but it is not the same as the mushroom I am describing here. I have seen it under loblolly pine in eastern Texas; it has a dry cap, and a reddish stem that is not particularly club-shaped. It is illustrated in Weber & Smith (1985) and in Metzler & Metzler (1992). I respectfully disagree with the application of the epithet pinophilus for this species; it is not very similar to the European species.
Description:
Ecology: Mycorrhizal with Engelmann spruce, and perhaps with other spruces and with firs; growing alone, scattered, or gregariously; summer and fall, in monsoon season; Rocky Mountains.
Cap: 10-30 cm at maturity; convex in the button stage, becoming broadly convex to nearly flat; greasy to tacky; bald; brownish red (oac 601) to reddish brown (oac 623); sometimes with a whitish bloom when young.
Pore Surface: Whitish at first, becoming yellowish to brownish yellow and eventually olive; not bruising; pores "stuffed" at first; with 2-4 circular pores per mm at maturity; tubes to 3 cm deep.
Stem: 10-18 cm long; 3-8 cm thick; swollen and club-shaped when young, becoming club-shaped or equal; finely reticulate over at least the upper portion; white or pale brownish; basal mycelium white.
Flesh: White; solid; unchanging when sliced, or staining slightly pinkish.
Odor and Taste: Taste nutty; odor not distinctive.
Chemical Reactions: KOH on cap red to orange to orangish; on flesh negative. Ammonia black on cap; negative on flesh.
Spore Print: Olive brown to brownish.
Microscopic Features: Spores 12-20 x 4-6 µ; smooth; subfusiform.
REFERENCES: For the taxon described here: States, 1990; Evenson, 1997. For Boletus pinophilus: Pilat & Dermek, 1973 (Saccardo, 1888; Moser, 1983; Breitenbach & Kränzlin, 1991; Hansen & Knudsen, 1992.) Herb. Kuo 07280606, 08150719.
Boletus pinicola, Boletus edulis var. pinicola, and Boletus aestivalis var. pinicola are synonyms of Boletus pinophilus.
