Summary:
Features include large size; tall, oval, white cap with large brown scales, the cap blackening at maturity; free, crowded gills that deliquesce; white silky stem; mild odor, black spore deposit; and habitat on lawns, roadsides, along trails or near compost heaps. In the scheme based on molecular evidence, this species remains in Coprinus with Coprinus spadiceisporus and Coprinus sterquilinus, while most of the Coprinus species are distributed to Coprinopsis, Coprinellus, and Parasola, (Redhead(49)). Van de Bogart has described three varieties in WA in addition to C. comatus var. comatus: var. parvus is distinguished by small size (cap 4-5cm tall before expansion and stem 5-6cm tall), and sterigmata of basidia are colorless and lack the refractile plug, var. excentricus has very eccentric germ pore and the spores are usually large (14-18 microns long), and var. caprimammillatus of which each fruiting body has some spores with apical germ pore and some spores with the germ pore at least somewhat eccentric. C. comatus is common in the Pacific Northwest.

Cap:
6.4-12cm high prior to expansion, 3.5-10cm across after expansion, ovate-oblong at first, then conic, then bell-shaped, and eventually revolute [upturned] or laciniate or both; white ground color with brown-tipped scales and all brown at top of cap, eventually most of the cap slowly blackening and the brownish scales and top becoming dark brown when old; smooth at top, the remainder squarrosely scaly, the fibrillose scales 0.2-0.9cm long and wide, numerous shallow plicate striations developing beneath the thick white universal veil and only becoming apparent when cap expands enough to dislodge some of veil from margin area, (Van De Bogart), 4-15(25)cm high, cylindric or columnar, expanding somewhat as margin becomes upcurved until more or less bell-shaped, then deliquescing from the bottom up; white with brown to pale cinnamon-brown or buff center, soon breaking up into shaggy, white to brown scales, often recurved when old; not viscid, margin striate when old and often tattered, (Arora)

Flesh:
thin and membranous except at top where it may reach up to 0.2cm thick, in stem fibrous but somewhat brittle, up to 0.2cm thick, (Van De Bogart), soft; white, (Arora)

Gills:
free and remote, crowded, subgills few or none, linear, 4-11.8cm x 1-1.2cm; white, then rose pink, then purple to gray-black, and finally soot-black; autolysis complete, (Van De Bogart), free or nearly so, very crowded; "at first white, then passing through delicate shades of pink, pinkish red, or vinaceous", finally black and inky, (Arora)

Stem:
7.5-19(32)cm x 0.35-2.1cm, widening towards base, base bulbous to abrupt, stem hollow, the lumen containing a loosely interwoven yarn-like hyphal thread in center; white; smooth, silky-bald, opaque, (Van De Bogart), 5-20(40)cm x 1-2cm, narrowing downward or with an enlarged, more or less pointed base, hollow or stuffed with a pith, cleanly separable from cap; white; smooth, (Arora)

Veil:
universal veil thick, smooth at top of cap, the remainder squarrosely scaly, the veil covering the cap entirely until late maturity when small parts of surface revealed by splitting, dislodgement or lysis of the veil elements; large, loose, white ring present, usually near stem base, which seems to be the edges of a fragile volva that is almost always attached more firmly to the cap margin than to the stem base and hence carried part way up the stem upon expansion, (Van De Bogart), partial veil membranous, "forming a small, white, movable, inferior ring" which often drops to base of stem or falls off, (Arora)

Odor:
faint odor of mushrooms (Van De Bogart)

Taste:
mild (Van De Bogart)

Microscopic spores:
spores 10.6-13.8(17.6) x 5.5-7.6(10) microns, smooth, mostly elliptic and round in cross-section, some broadly elliptic, germ pore apical, 1.8-3.0 microns in diameter, apiculus usually large and prominent but sometimes small, "medium to deep brown or smoky brown or smoky grey-brown in 3% KOH", contents "guttulate or not, often with a finely granular appearance in 3% KOH"; basidia 4-spored, trimorphic, short clavate and 23.8-33.0 x 11.5-15.0 microns, long clavate and 35.0-46.5 x 9.0-16.2 microns, subululiform to ululiform and 45.0-67.5 x 11.3-17.5 microns, the sterigmata with conspicuous, dark, refringent plugs inside them; cheilocystidia spherical, ovate, clavate, and short-ellipsoid, often with one or more types lacking, spherical 13.9-35.0 microns in diameter, ovate 25.0-50.0 x 19.0-25.0 microns, clavate to ellipsoid 25.0-50.0 x 13.9-28.0 microns, colorless, smooth, a few with a short pedicel 1.0-3.0 microns long, no other cystidia present; clamp connections "almost always present on some universal veil hyphae" and often present on stem hyphae, but rarely present on cap surface hyphae, (Van De Bogart), spores 10-16(18) x 7-9 microns, elliptic, smooth, with germ pore, (Arora)

Spore deposit:
soot black (Van De Bogart)

Notes:
There are collections at the University of Washington from WA, OR, AK, CA, NY, UT, and VA. There are collections at the University of British Columbia from BC. It is widespread in North America. Breitenbach(4) give distribution as America, Europe, Asia, North Africa, and Australia.

EDIBILITY

delicious, may rarely react with alcohol like C. atramentarius, (Arora)