On the type of Coprinus colosseus Van De Bogart
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Original description
Coprinus colosseus Van De Bogart in Mycotaxon 4: 265. 1976 (The genus Coprinus in Western North America, part 1: sect. Coprinus). Holotype: North America: state Washington, Redmond, 2 May 1966, F. Van De Bogart 143 (WTU).

Pileus oblong-oval at first, then narrow conical, then narrow campanulate, then broadly shallow campanulate, and eventually laciniate-revolute. Prior to expansion 13.0-25.4 cm in length and after expansion 8.0-14.0 cm broad, the smaller size due to autodigestion during expansion. White with brownish-tipped scales and pale brown pileal apex at first and then gradually darkening with maturity and autolysis. Plicate striation limited in development, involving little or none of the lamellar trama. Surface covered with a universal veil of rather small scales that are white to white with brownish tips. Scales firmly attached when pileus is immature but becoming loose and easily removable as pileus matures. Flesh mostly thin and membranous but up to 3.0 mm in thickness at apex. Stipe hollow, the lumen containing a loose yarnlike thread of loosely interwoven filaments. Almost equal but with a slight tapering from base to apex, 35.0-50.5 x 1.5-2.5 cm, the base abrupt and embedded up to 8 additional centimeters into the soil. A small loose annulus present on some specimens. Surface seeming smooth and glabrous. White at first, then as spores are produced and autolysis proceeds the apical flesh slowly blackening internally as well as externally. Flesh opaque, coarse and fibrous. Rhizomorphs of compact white hyphae penetrating about 15.0 cm into the substrate from some specimens. Lamellae linear, almost all long, 8.0-25.0 x 1.5-2.3 cm, free but attached to a small collarium. Extremely crowded at first and remaining crowded throughout sporulation and lysis, pale but becoming soot black. Autolysis almost complete, nearly the entire pileus affected. Odor and taste none.
Spores ovate in dorsal view and ovate-ellipsoidal in lateral view, somewhat flattened, 16.8-20.0 x 9.8-13.7 x 8.4-11.3 µm, apiculus large and conspicuous, germ pore somewhat eccentric to very eccentric 1.8-3.1 µm in diameter. Color en masse soot black, microscopically an extremely dark smoky black color in 3% KOH. Contents seeming minutely guttulate or granular in 3% KOH. Wall smooth. Basidia trimorphic, short clavate and 31.5-35.5 x 16.0-18.0 µm, long clavate and 42.5-48.5 x 17.0-18.0 µm, very long clavate-pedicellate and 54.0-65.0 x 19.0-20.0 µm, all four-spored, all sterigmata with a large refractive or pigmented plug. Cheilocystidia globose or ellipsoidal-ovate, globose 20.0-37.5 µm in diameter, ellipsoidal-ovate 35.0-50.0 x 20.0-25.0 µm, hyaline, smooth. No other cystidia present. Pileal surface of radially oriented hyphae. Universal veil scales composed of cylindrical septate hyphae, mostly swollen and somewhat constricted at the septations, smooth, hyaline, thin-walled cells 17.5-165.0 x 5.0-38.0 µm. A thin tomentum present at base of stipe, composed of slender, nonswollen, hyalin, smooth, thin-walled, branched and interwoven septate hyphae, the cells tending to be long and straight. Clamp-connections rare on stipe cuticle.
Habitat. Terrestrial, on loose, crumbly soil in a dense brushy scrub frondose forest, in large loose clumps, rare.

This species is well marked by its huge overall size, large spore size, and by the darkening of the stipe apex. The last two features it shares with C. sterquilinus, a coprophilous species which is much smaller.

Observations
Spores [20,1,1] 16.9-21.1 x 10.9-13.6 x c. 9-11.5 µm, ellipsoid or ovoid, with rounded base and apex, and eccentric, c. 2.5 µm wide germ pore, very dark red-brown; Q = 1.45-1.60, av. Q = 1.55; av. L = 18.8, av. B = 12.2 µm. Basidia 40-65 x (14-)16-20 µm, 4-spored, surrounded by 7-13 pseudoparaphyses. Pleurocystidia absent. Cheilocystidia 20-50 x 20-35 µm, (sub)globose. Pileipellis hyphoid. Veil made up of hyphoid, thin-walled elements, 30-150 x 8-30 µm, in part somewhat inflated, constricted at septa; terminal cells clavate, ellipsoid or subcylindric. Clamp-connections not found.
Notes: Two rather bad basidiocarps were available. The basel ring described by Van De Bogart failed on both of the specimens.
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