Features of Coprinopsis atramentaria group include a lead-gray to brownish, radially lined cap that deliquesces, a relatively thick stem, and often clustered growth. Van de Bogart''s description is for var. atramentaria, other varieties are as follows: var. acuminata as var. atramentaria except that a prominent umbo is present at cap apex, and var. crassivelata as var. atramentaria except that veil thick and often forming areolate patches [cracked like dried mud]. The former has been raised to species status as Coprinopsis acuminata which according to Siegel(2) is similar in appearance but "typically smaller and has a more conical cap with a small, rounded umbo and smaller spores; it is more often found in forested settings". Another species in the group is Coprinopsis romagnesiana which "has a slightly scaly cap (at least in age) and small blackish scales on the lower stipe", (Siegel). C. atramentaria group is common in the Pacific Northwest.
2-6.5cm high before expansion, 3.0-8.0 across after expansion, shape variable at first, spherical, short acorn-shaped, ovate, subconic [nearly conic] and then broadly rounded conic, often finally revolute [upturned] or laciniate; light grayish tan and medium brown at top at first, becoming darker prior to blackening when it lyses; small poorly developed pleated-striation present on some and not others, ranges from smooth and bald to partially covered with small, brown, closely adherent scales, (Van De Bogart), 2-8cm high and/or broad, spherical or ovoid and often somewhat lobed when young, becoming conic to bell-shaped, or in old age convex, deliquescing from margin to center; grayish brown to grayish tan when young (center often browner or with small brown scales and margin sometimes pallid) becoming lead gray to inky gray when old; "dry, smooth or with silky whitish fibrils" when young, margin striate or grooved, usually tattered or splitting when old, (Arora)
ranging from thin and membranous at cap margin to 0.3cm thick at top in large specimens, in stem thick and fibrous, sometimes brittle, sometimes rather tough, 0.1-0.35cm thick, (Van De Bogart), thin, soft; pallid or grayish, (Arora)
free, extremely crowded, narrowly ellipsoid, 4.5-6.2cm x 1.4cm; dingy white, then brown, and finally deep brownish black; destroyed by autolysis, (Van De Bogart), "free or nearly free, crowded"; "at first white, soon gray or with pinkish to vinaceous tints", finally black and inky, (Arora)
3-17.5cm x 0.25-1cm, hollow, slightly enlarged about 1/3 of the way up, where there is an annular ring or flange-like zone; white above the enlarged area, white with small brown appressed scales below it; smooth and often silky above the enlarged area, (Van De Bogart), 4-15(20)cm x 0.6-1.5cm, "equal or with narrowed or enlarged base", hollow; white or with grayish to brownish fibrils in lower part, may even have a rudimentary volva at base, (Arora)
universal veil forms small brown closely adherent scales on cap and stem base, similar hyphae making up the annular ring-like zone on the enlarged area of the stem, (Van De Bogart), partial veil fibrillose, may be evanescent or leave a median to basal ring or ridged zone on stem, (Arora)
none (Van De Bogart)
mild (Van De Bogart)
spores (6.2)8.1-10.0(11.4) x (3.7)4.4-6.5 microns, broadly ovate, narrowly ovate, or elliptic, round in cross-section or nearly so, smooth, germ pore apical, 0.6-2.2 microns in diameter, apiculus of medium to small size, usually visible, spore light to medium brown or smoky brown, sometimes also with a purple tint in 3% KOH, almost all guttulate; basidia 4-spored, dimorphic, with only the first two basidial types present, or trimorphic, rarely tetramorphic, short clavate and 12.0-17.0 x 7.5 microns, long clavate and 17.5-22.5 x 7.5-8.8 microns, sphaeropedicellate to ululiform and 25.0-28.8 x 7.5-10.0 microns, very long ululiform and 35.6-37.4 x 8.8 microns; pleurocystidia 59.0-214.0 x 16.5-75.0 microns, subcylindric to ellipsoid, smooth, colorless, occasionally with a pedicel 1.0-7.0 microns long, cheilocystidia spherical, 13.8-50.0 microns in diameter or ovate to long ellipsoid, 74.8-100.0 x 25.0-56.3 microns, smooth, colorless; no other cystidia present; clamp connections present on stem, usually on the cap surface, occasionally in the gill trama, (Van De Bogart), spores 7-12 x 4-6 microns, elliptic, smooth, (Arora), spores 6.5-10.5 x 4-6.5cm (Siegel)
deep brownish black to almost black (Van De Bogart), black (Arora)
It is specifically noted for WA (Van De Bogart). Collections from BC are at the University of British Columbia, from OR at Oregon State University and from WA and ID at the University of Washington. Desjardin(6) illustrate for CA. Breitenbach(4) give the distribution as North America, Europe, Asia, North Africa, and Australia.