SUILLUS ACERBUS Smith and Thiers, Contr. Toward a Monogr. of N. Am. Sp. of Suillus, p. 103. 1964

Illustrations: See Microfiche No. 37

Pileus 8-13.6 cm broad when mature, when young convex, becoming plane to plano-convex with a shallow to moderately deep depression on the disc, often undulating to highly irregular toward the margin; surface viscid, glabrous to fibrillose or fibrillose-scaly, often streaked with gluten when older; color highly variable, reddish to brown ("tawny" to "ochraceous-tawny" to "hazel" to "buckthorn brown" to "cinnamon" to "cinnamon-buff"), in some these colors appear overlain with grayish pigments, giving a dark brown or gray appearance, with age unchanging or fading to light brown ("cinnamon-buff" to "buffy brown"), or often a slightly paler mixture of some of the above colors, frequently with a greater concentration of darker pigments toward the margin; margin entire, incurved, glabrous. Context 1.5-2.5 cm thick on the disc, white, staining yellow in irregular areas and pinkish brown ("avellaneous" to "testaceous") around larval tunnels. Taste unpleasant, somewhat harsh and acid; odor not distinctive.

Tubes 0.5-1 cm long, adnate to arcuate-decurrent, typically becoming decurrent with age, when young white to pale yellow ("colonial buff" to "deep colonial buff") to less frequently pallid ("pale pinkish buff"), becoming yellow ("reed yellow" to "primrose yellow" to "chamois") with age, not changing when bruised or exposed; pores not exceeding 1 mm broad, angular, concolorous, unchanging when bruised.

Stipe 4-10 cm long, 1.5-2.5 cm thick at the apex, equal to slightly enlarged at the base, straight or frequently bent or crooked, solid; surface dry, glabrous but covered with large, inconspicuous to conspicuous glandulae that become brown ("cinnamon" to "ferruginous") with age or when handled, some obscure reticulation apparent at the apex and often with irregular longitudinal lines forming a crude network toward the base, no true raised reticulation present; color white to very pale yellow ("ivory yellow"), changing with age or when handled to yellow ("Naples yellow" to "amber yellow"), not changing in same intensity in all parts of the stipe; no annulus. Context white, typically staining yellowish when exposed.

Spore print dull brown. Spores 9.3-12 X 3.3-4 Ám, hyaline to pale ochraceous in KOH, smooth, thin-walled, cylindric to subellipsoid in face view to subventricose in profile.

Basidia 24-29 X 5-8 Ám, hyaline, clavate, contents granulose in KOH, four-spored. Hymenial cystidia 30-46 X 7-10 Ám, fasciculate, scattered to very rare, found only near the pores of the tubes, basal portion often staining dark brown in KOH, apical portion remaining hyaline, occasionally staining vinaceous; no solitary cystidia seen.

Tube trama hyaline, divergent from a distinct mediostratum, subgelatinous, hyphae up to 7 Ám wide. Pileus trama interwoven, homogeneous. Pileus cuticle differentiated as an interwoven broad (300 Ám) ixotrichodermium, contents of hyphae appear brownish in KOH, outermost hyphae appearing somewhat differentiated and incrusted, hyphae up to 3.5 Ám wide; hypodermium well differentiated and the hyphae incrusted, interwoven and dark brown in KOH. Stipe cuticle gelatinous with massive clusters of darkly staining (brown to dark vinaceous) caulocystidia similar to the other cystidia. Clamp connections absent.

Chemical reactions KOH-cuticle red, context reddish, tubes black; NH4OH-context vinaceous, tubes red; HNO3 and HCl-context pale yellow; H2SO4-tubes dark red; FeSO4-context and tubes pale gray.

Habit, habitat, and distribution Gregarious to sometimes cespitose in soil under Monterey pines. Known only from the San Francisco Bay Area; sometimes abundant in the Presidio in San Francisco. It has not been found associated with any other of the numerous pines or conifers of the coastal forest.

Material studied Contra Costa County: Thiers 9687. Marin County: Shervanick 358. San Francisco County: Gleason 1-5-65; Hanks 11-10-64; Jordan 1019; Thiers 9685, 9686, 24518, 24537, 26887, 26962, 27065. San Mateo County: Thiers 11773, 12136; Torbett 11-16-64.

Observations This species is characterized by the brown to reddish-brown pileus, which appears granulose or fibrillose to tomentose, the absence of any type of veil, the unpleasant taste, and the relatively long spores. Suillus pungens, which also forms mycorrhizal associations with Monterey pine, shows a partial veil and white to gray color in the pileus when young. Suillus acerbus is possibly most clearly related to S. granulatus, which has smaller spores and a mild taste.

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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