On the type of Coprinus spadiceisporus
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Original description
Coprinus spadiceisporus Van De Bogart in Mycotaxon 4: 245. 1976 (The genus Coprinus in Western North America, part 1: sect. Coprinus). Holotype: North America: state Washington, exact locality and date unknown, F. Van De Bogart 217 (WTU).

Pileus at first ovate-ellipsoidal, then conical, then campanulate, and eventually somewhat revolute, when unexpanded from 3.0-3.8 cm long, expanding to 5.0 to 6.0 cm wide. Whitish when young but soon grey from ripening spores, the apex pale brownish, soon entirely dark greyish brown, except the apex which remains paler brown. Radial pileal striations apparent even at young stage and soon developing into plicate striations. Surface covered with a universal veil of small somewhat appressed scales of dingy or dirty white color, becoming much looser in age and more scattered but even then more or less persistent. Flesh rather thin and membranous. Leaves and debris stuck to pileal surface. Stipe hollow, rather stout for Coprinus, 10.0-12.0 cm x 5.0-8.0 mm. Prominent, loose, white, felty annulus present, about 1 mm in width. Hollow center filled with a weblike mass of loose hyphae. Outer surface smooth and glabrous except for a loose tomentum of woolly hairs at the base. White in color at first but soon darkening to light brownish over most of its length and becoming dark, almost black near the apex, opaque. Flesh rather thick and fibrous for a Coprinus. Lamellae lanseolate, 2.5-4.0 mm broad, free and remote, crowded, dark brownish black when mature. Autolysis complete.
Spores ovate-ellisoidal, slightly flattened, basal end broader than apical end, 8.1-10.0 x 6.2-6.9 x 5.0-5.6 µm, apiculus and germ pore both prominent, germ pore eccentric, 1.5-2.0 µm in diameter. Color dark blackish brown en masse and a clear translucent chestnut brown microscopically in 3% KOH. Wall smooth. Basidia trimorphic, short clavate and 12.5-17.5 x 10.0-11.2 µm, long clavate and 20.0-25.0 x 10.0-11.2 µm, ululiform and 28.7-35.0 x 10.0-11.2 µm, all four-spored. Cheilocystidia globose to more or less ovate, 15.0 µm in diameter to 42.5 x 30.0 µm intermixed with thin filamentous hyphae on gill edge. No other cystidia present. Pileal surface a cutis of radially oriented hyphae. Universal veil scales composed of fibrils aligned parallel to each other and composed of chains of unbranched, often swollen cells 6.2-20.0 µm in diameter, often constricted at the septations and then catenulate, also tending to break up into single loose cells. All cells of the universal veil with smooth, thin, hyaline walls, and all adjacent cells of the universal veil tending to be of similar size and shape. Clamp-connections present on the hyphae of the stipe surface and occasionally on the universal veil.
Habitat. Coprophilous, on rabbit or deer dung.

This species shares a peculiar feature with two other species of section Coprinus, C. sterquilinus and C. colosseus, namely, the discoloring and eventual blackening of the apical portion of the stipe flesh. The ovate, flattened spores with their clear light brown color seem distinctive.

Observations:
Spores [20,1,1] 8.2-10.3 x 5.8-7.3 µm, ovoid or slightly mitriform with rounded or conical base and rather truncate apex, and slightly eccentric, 1.6-1.8 µm wide germ pore, dark red-brown; Q = 1.25-1.45, av. Q = 1.35; av. L = 9.1, av. B = 6.7 µm. Basidia 22-42 x 10-12 µm, 4-spored, surrounded by 5-8 pseudoparaphyses. Pleurocystidia absent. Cheilocystidia 30-50 x 17-30 µm, (sub)globose, ellipsoid or oblong. Pileipellis hyphoid, made up of mainly cylindrical hyphae; elements 50-130 x 10-20 µm. Veil made up of cylindrical, thin-walled elements, 30-180 x 6-25 µm, somewhat constricted at septa; terminal cells cylindrical with rounded or tapering apex. Only pseudoclamps found.

Notes: The material in this collection exists of one young specimen and a primordium at a small twig. White mycelium is still visible at the base of the stipe. The apex of the sterigmen is dark coloured as found in C. roseistipitatus.
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