Summary:
Features include 1) an olive-brown to yellow-brown, glutinous cap that appears streaked-fibrillose below the gluten and typically has hanging veil remnants on the margin, 2) whitish to pale yellow flesh that is unchanging or stains dingy pinkish, 3) olive-grayish-buff to yellowish pores that are often beaded with droplets, 4) whitish to yellowish stem, 5) a large band-like annulus on stem, and 6) conspicuous glandular dots on stem that become blackish when old. Regarding the synonymy of Suillus subolivaceus with Suillus acidus, Nguyen(3) wrote, "The /acidus clade contained sequences from the holotypes of S. lutescens A.H. Sm. & Thiers and S. subolivaceus A.H. Sm. & Thiers. We were unable to obtain a sequence for the type of S. acidus (Peck) Singer, but all specimens of what we identified as S. acidus based on morphology fit into this clade. (Smith and Thiers 1964a) thought that S. lutescens was closely related to S. acidus, and our sequence data support that relationship. To confirm the correct name for this clade, the holotype sequences for S. acidus will need to be obtained. Given the age of the holotype (before 1905), epitypification may be the best approach." When accessed on February 18, 2018, the online Species Fungorum gave the current name as Suillus acidus, and MycoBank gave Suillus subolivaceus as separate or a variety of Suillus acidus. Suillus acidus is rather common in WA and OR, (Smith(34) as S. subolivaceus).

Chemical Reactions:
cap surface stains dark brown to black with application of KOH, flesh stains lavender with application of KOH and grayish brown with FeSO4, (Bessette)

Odor:
not distinctive (Bessette), slight (Smith)

Taste:
not distinctive (Bessette), acid (Smith)

Microscopic:
spores 8-11 x 3-4.5 microns, subfusoid [somewhat spindle-shaped], smooth, pale ochraceous, (Bessette), spores (8)9-11 x 3-4(4.5) microns, typically subfusoid, smooth, pale ochraceous to greenish transparent in KOH, walls slightly thickened; basidia 4-spored, 18-23 x 5-6(7) microns, clavate, colorless in KOH; pleurocystidia 40-55 x 6-11 microns, "subcylindric to narrowly clavate or subfusoid with obtuse apices", as revived in KOH either colorless or with yellowish brown content, the cystidia in fascicles with rusty brown incrusting pigment around the base as revived in KOH, cheilocystidia "scattered and in groups, like the pleurocystidia but often longer and frequently (as revived in KOH) with so much surrounding encrusting pigment that the cystidia themselves are obscured"; cap epicutis a thick layer of gelatinous hyphae 3-7 microns wide "and with some bister incrusting pigment seen as revived in KOH, the hyphae as revived appearing to be appressed and rather crooked"; caulocystidia up to 70-x 12 microns but mostly 40-60 x 6-10 microns, "content of most of them dark yellow brown as revived in KOH", "in dense fascicles and with a copious amount of incrusting pigment"; clamp connections none, (Smith)

Spore Deposit:
brown (Bessette), dingy cinnamon (Smith)

Notes:
Suillus acidus has been found in WA and OR (Smith), the northern Rocky Mountains, south to OR and ID, (Bessette), and it has been recorded from BC (Schalkwijk-Barendsen). A collection from BC is at the University of British Columbia, and a collection from AK at the University of Washington (both as S. subolivaceus). The University of Washington has collections from WA and ID, and Oregon State University has collections from OR (all as S. subolivaceus). It is found in MT (L. Evans, pers. comm. as S. subolivaceus).

EDIBILITY

yes (Bessette)

Synonyms and Alternate Names:
Sparassis crispa (Wulfen) Fr. (misapplied name)