Summary:
{See also Blackening Russulas Table.} This may be a synonym of Russula nigricans (see below). Russula dissimulans is characterized by 1) a whitish cap that becomes smoky brown then black, 2) an inseparable cap skin which is viscid when young but soon dry, felty or velvety, 3) hard flesh that turns red then smoky brown to black, 4) close to crowded gills, 5) a short white stem that becomes brown then black, 6) a mild odor, 7) a mild to slightly peppery taste, and 8) a white spore deposit. |In the original description, Shaffer said (with Latin names italicized), "This new species, R. dissimulans, and R. nigricans are closely related, and the former has previously passed in North America as the latter. Singer (1958) recognized that the American representatives of the R. nigricans complex are different from the European and proposed that they be treated as a subspecies of R. nigricans on the basis of their consistently larger number of lamellae. There are also other differences between the two taxa, and although none of them can be considered absolutely definitive, their number indicates that the American representatives should be considered a separate species (Table 1)". The content of the table is reproduced below in the SIMILAR section. |However, Buyck collected and sequenced material in the Pacific Northwest that was a genetic match for Russula nigricans from the type area, and corresponding eastern North American DNA seems to be different from that in the Pacific Northwest, (D. Miller, pers. comm.). It is not yet established by DNA that there is another distinct species that would correspond to R. dissimulans and it could even prove to be a synonym.

Cap:
6.5-18cm across, depressed in center; "whitish when young, soon smoky brown and eventually black"; "slightly viscid when young but soon dry, felty or velvety", cracked into areolae when old, not peeling, margin even, (Woo), 6.5-18cm across, "when young convex with depressed disc and inrolled margin", expanding to flat-convex with depressed disc, the margin becoming raised and arching when old and the cap then more or less funnel-shaped; chalky white when young, soon becoming brown, drab, fuscous, or black almost overall; "slightly viscid when young, but soon dry, or dry from the beginning", matte, bald to minutely felted, with margin at times rugulose [finely wrinkled], often becoming areolately cracked, cap skin not separable or separable up to one fourth the distance to the center, margin not striate, (Shaffer)

Flesh:
hard; "white, turning red when cut, then smoky brown to black", (Woo), thick, 1-2cm, hard-brittle; white, when cut changing slowly through vinaceous-cinnamon to brick red and then eventually through drab to fuscous or black, (Shaffer)

Gills:
close to crowded, regular subgills; "light yellow, blackening when injured", (Woo), adnexed-adnate to decurrent, close to subdistant, subgills abundant, 1-3 between neighboring pairs of gills, narrow to moderately broad, 0.4-1.4cm, acute near cap margin, broadest near middle, thick, brittle, not forked or only rarely so, rarely poroid-anastomosing at the stem, prominently interveined; light yellow, becoming dingy when old, when bruised changing through the same general color series as the cap flesh; edges entire, (Shaffer)

Stem:
short, "white becoming brown, then black", (Woo), 4-8cm x 2-4.5cm at top, at base 1.8-4cm wide, narrowing to the base which may be obliquely subbulbous, or flared slightly at top and subequal or widening to the base below, straight or curved, round in cross-section or slightly flattened, solid or stuffed, sometimes hollow when old; when young white, when old drab to fuscous or black almost overall, when bruised changing through the same general color series as the cap flesh; bald, unpolished, even or uneven, (Shaffer)

Odor:
none (Woo), slight or none (Shaffer)

Taste:
mild to slightly peppery (Woo), mild or becoming slightly or burning peppery (Shaffer)

Microscopic spores:
spores 7.7-10.8 x 6.5-9 microns, ornamentation Patterson-Woo type B-2, C-2, (Woo), spores 7.7-10.8 x 6.5-9 microns, usually elliptic to broadly elliptic, occasionally nearly round or oboval, ornamentation 0.1-0.5(0.7) microns high, "on a few spores consisting of warts which are almost completely isolated, on most spores of warts which are sometimes isolated, especially around the plage, but usually connected by fine to moderately heavy lines, the whole forming a nearly complete to complete reticulum"; basidia usually 4-spored, rarely 1-, 2-, or 3-spored, 39-67 x 7.2-12 microns, clavate; pleuropseudocystidia abundant, arising in the subhymenium or outer trama, "embedded, not projecting, or projecting slightly to moderately", 35-86 x 4-8.6 microns, usually cylindric to narrowly fusoid or clavate, rarely fusoid-ventricose, "with apices usually rounded or capitate, occasionally bearing a small bulb or stub, rarely acute", "at times slightly enlarged and/or narrowed a few times along their lengths", often curved basally, "nearly empty to filled with refractive contents", cheilocystidia common to very abundant, "not projecting beyond the level of the basidiole tips or the elongate ones projecting prominently", 16-110 x 3.3-10.6 microns, subcylindric (and then sometimes filamentous and flexuous [wavy]), clavate, fusoid, or lanceolate, colorless or with brown sap or with refractive contents, often arising from chains of inflated tramal cells, the elongate cheilocystidia sometimes occurring about 250 microns up the gill faces, (Shaffer), cap cuticle 115-200 microns thick, hyphae not embedded in a gelatinous matrix, epicutis interwoven, with free hyphal tips, pileocystidia absent, (Thiers)

Spore deposit:
white, Crawshay A, (Woo), white (Shaffer)

Notes:
Shaffer examined collections from WA, OR, ID, CA, MI (including holotype), NC, and VT. Roberts, C.(2) reports it from Vancouver Island in BC but expressed reservations about two of the criteria Shaffer used to describe it as separate from R. nigricans - while Shaffer''s account of gill spacing and spore size for European material are distinct from his concept of R. nigricans in Europe, accounts of other European authors are not as distinct. The collections of C. Roberts from Vancouver Island have spore ornamentation of a height fitting R. dissimulans rather than R. nigricans.

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