Illustrations: See Microfiche No. 3

Pileus 3-6 cm latus, uvidus vel subviscidus, glaber, rubidus vel obscure rufobrunneus. Contextus puniceus, immutabilis. Sapor et odor mitis. Tubuli 4-8 mm longi, subgalbani, tactu immutabiles; pori 1 mm lati, concolores tactu immutabiles. Stipes 8-10.5 cm longus, 1-1.5 cm crassus, siccus vel uvidus, glaber, subalutaceous vel alutaceus; contextus concolor tactu immutabilis. Sporae 13.5-15.5 X 4.5-5.5 µm, amyloideae, ellipsoideae vel fusoideae. Cystidia 30-48 X 7-15 µm, clavata vel subvesiculosa vel fusoideo-ventricosa. Cuticula e hyphis rectis composita. Holotypus (no. 26903) a H. D. Thiers lectus prope Jackson State Forest, Mendocino County, November 14, 1970; in Herbarium San Francisco State University conservatus.

Pileus 3-6 cm broad at maturity, convex when young, unchanging or becoming plano-convex to plane with age; surface moist to subviscid to viscid but never strongly so, glabrous during all stages, not rimose or areolate, evenly colored dark red to dark reddish brown ("Kaiser brown" to "dragons-blood red") when young, darkening to deep reddish brown ("Hay's russet") with age; margin entire, concolorous. Context 8-15 mm thick, pink ("alizarine pink" to "old rose"), unchanging when exposed. Taste and odor mild.

Tubes 4-8 mm in length, deeply to shallowly depressed, pale greenish yellow ("seafoam yellow" to "seafoam green"), not changing to blue when bruised; pores less than 1 mm broad, angular, bright greenish yellow ("lime green" to "reed yellow"), when bruised unchanging or darkening slightly or, less commonly, fading to pale greenish yellow ("seafoam yellow").

Stipe 8-10.5 cm long, 1-1.5 cm thick at the apex, clavate to subclavate, solid, surface dry to moist, not lubricous or viscid, glabrous during all stages of development; pale tan to tan ("warm buff" to "light buff"), sometimes with a reddish flush at the apex. Context white to concolorous with the surface, unchanging when exposed.

Spore print dark olive brown. Spores 13-5-15.5 X 4.5-5.5 Ám, pale ochraceous in KOH, distinctly amyloid in Melzer's, ellipsoid to fusoid in face view, ventricose to inequilateral in profile, occasionally with truncate apex, walls smooth, thin.

Basidia 23-27 X 6-8 Ám, hyaline in KOH, four-spored, clavate. Hymenial cystidia 30-48 X 7-15 Ám, scattered, hyaline in KOH, clavate to subvesiculose to obscurely fusoid-ventricose, walls thin, not incrusted.

Tube trama hyaline in KOH, divergent, hyphae 5-6 Ám wide. Pileus trama interwoven, homogenous. Pileus cuticle differentiated as a trichodermium of erect hyphal tips forming a turf, not gelatinizing in KOH, septate, terminal cells not at all or only slightly differentiated, not incrusted, pale yellow in KOH, bright red in Melzer's. Stipe cuticle similar to that of the pileus. Clamp connections absent.

Chemical reactions KOH-context white, cuticle dark brown; HCl-context of stipe yellow; FeSO4-context gray.

Habit, habitat, and distribution Gregarious in soil in dense mixed hardwood-conifer forest. Known only from the coastal forests of Mendocino County.

Material studied Mendocino County: Cole 11-14-70; Thiers 26903 type.

Observations The discovery of this species adds another to the growing list of boletes with amyloid spores. Recently Smith described Tylopilus amylosporus from Northern Idaho, but it has a dark reddish-brown spore deposit and at least some of the spores are truncate. Other species have been found to give at least fleetingly positive amyloid reactions in one or more parts of the basidiocarp. Boletus amyloideus is one of the few species known, however, in which all spores show this reaction and in which the reaction is strong enough to give a blue-black discoloration to the hymenium or to spore masses. It is further distinguished by the reddish color of the pileus, which is subviscid to viscid in wet weather, the bright-greenish-yellow tubes, and the failure of the context to change to blue when exposed.

Edibility unknown.

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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