GYROPORUS CASTANEUS (Fries) Quélet, Enchir. Fung., p. 161. 1886
Boletus castaneus Fries, Syst. Mycol. 1:392. 1821
Illustrations: See Microfiche No. 24
Kawamura, S., Icones of Japanese Fungi, pl. 248.
Leclair, A., and H. Essette, Les Bolets, pl. 70.
Romagnesi, H., Nouvel Atlas des Champignons, pl. 137.
Singer, R., Die Rohrlinge, Teil I, pl. II, figs. 1-4.
Smith, A. H., The Mushroom Hunter's Field Guide, p. 75.
Smith, A. H., and H. D. Thiers, The Boletes of Michigan, pls. 2-4.
Snell, W. H., and E. A. Dick, The Boleti of Northeastern North America, pl. 7.

Pileus 3-7 cm broad, obtuse to convex when young, becoming broadly convex to plano-convex to plane or depressed with age; surface dry, glabrous to finely tomentose to pulverulent, often rimose or areolate-rimose with age, colored brown to tan to pinkish brown ("Mikado brown" to "orange-cinnamon" to "pinkish cinnamon" to "pecan brown" to "antique brown"); margin entire, but becoming rimose or split, incurved, becoming decurved or flared. Context 5-7 mm thick, white, unchanging when exposed; taste and odor mild.

Tubes 3-5 mm long, shallow to deeply and broadly depressed around the stipe, white when young, becoming yellow ("Naples yellow" to "barium yellow" to "amber yellow") at maturity, unchanging or darkening slightly when bruised; pores one to two per millimeter, angular, radially elongate near stipe apex, concolorous with tubes.

Stipe 2-4 cm long, 0.5-1.5 cm thick at the apex, equal to tapering toward the apex, hollow in basal portion; surface dry, unpolished, glabrous to tomentose to velutinous, colored similarly to the pileus-tan to brown to pinkish brown. Context white, unchanging.

Spore print yellow. Spores 10-12.5(14) X 5-6 Ám, hyaline to pale yellow in KOH, ochraceous in Melzer's, ellipsoid, inequilateral in side view, smooth, thin-walled.

Basidia 30-35 X 8-14 Ám four-spored, clavate, hyaline to pale yellow in KOH. Hymenial cystida 30-45 X 7-11 Ám abundant, hyaline, thin-walled, fusoid to obscurely fusoid-ventricose.

Tube trama hyaline, divergent. Pileus trama nonamyloid, interwoven, hyphae 6-8 Ám. Pileus cuticle differentiated as a layer of cystidioid cells forming a tangled trichodermium. Stipe cuticle more or less similar to the pileus cuticle, hyphae of context transversely oriented. Clamp connections present.

Chemical reactions Singer reports the following data: Metol-positive; phenol-chocolate brown; lactic acid-cuticle purple red; guiaic-context slowly and weakly blue green.

Habit, habitat, and distribution Gregarious in sandy alluvium along the delta of the Sacramento River. So far it has been found only under oaks. Although relatively common in the eastern half of the United States, this is apparently a very rare bolete on the west coast. It is known from only a few collections in California. These were made in the same place and the basidiocarps probably developed from the same mycelium. A few collections have also been made in Oregon and Washington.

Material studied Solano County: Sundberg 1209, 1346, 1488.

Observations Gyroporus castaneus, the only representative of this genus known from the state, is easily recognized by its small size, white tubes that become yellow as the spores mature, and the yellow spore deposit. In addition, the stipe and pileus are of the same pinkish-brown color. It is not likely to be confused with any other known bolete from California.

All collections cited above are made by Dr. Walter Sundberg, and this description has been drawn largely from his notes.

Although too small and rare in this state to be of any significance, in Europe, where it is often abundant, it is considered edible and choice.

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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