Common Ink Cap

Coprinopsis atramentaria is one of the most frequently encountered inkcaps of parks, gardens and roadsides. It was long placed in Coprinus, but molecular work split that assemblage apart, and this species now sits in Coprinopsis within the family Psathyrellaceae, alongside Coprinopsis lagopus and Coprinopsis picacea. True Coprinus, which contains Shaggy Mane, turned out to belong in a quite different family.

Like its relatives it deliquesces, dissolving its gills into an inky black fluid from the cap margin upward as the spores ripen. The process is quick: a fruiting body that is grey and firm in the morning may be a black smear on the ground by evening. The dark pigment in the liquid is largely the spore mass itself.

It is distinguished from other grey inkcaps chiefly by its size and habit. Fruiting bodies are relatively substantial for the genus, with thick stems, and they emerge in dense clustered tufts of a dozen or more from buried roots and rotting wood, often pushing up through lawn turf or gravel some distance from any visible stump.

Cap

3-8 cm across and up to 7 cm tall, at first a smooth grey egg, expanding to a broad bell or cone and eventually flattening as it dissolves. The colour is grey to grey-brown with a distinctly paler ochre-brown or tan centre. The surface is smooth or covered near the disc with small brownish flattened scales, and is marked with fine radial fibrils. The margin is grooved, often irregular or lobed, and typically splits into several radiating tears before deliquescence begins.

Gills

Crowded, broad, free to narrowly attached, white when young, then greyish, then black as they liquefy from the cap margin upward. In a clustered tuft, individual fruiting bodies are frequently at different stages, so white, grey and inky gills can be seen side by side.

Stipe

7-17 cm tall and 0.8-1.5 cm thick, white, smooth, hollow and fairly stout for an inkcap, tapering slightly upward. There is no true skirt-like ring, but a low ridge or narrow rim of veil tissue is often present near the base, and the base itself may be slightly swollen and joined to neighbouring stems in the tuft.

Flesh & spore print

Flesh thin, whitish, soft, becoming watery grey as the fruiting body matures. Smell faint. The spore print is black to blackish-brown, and the spores are smooth, ellipsoid and dark, each with a distinct germ pore.

The species is saprotrophic on buried wood: old tree roots, stumps, rotting timber, garden debris and construction fill. Because the wood is often invisible below ground, the tufts appear to be growing in bare soil, lawn or gravel, and are a familiar sight on roadside verges, in parks, on landscaped ground and around felled trees. It shows a preference for enriched, disturbed and compacted sites.

It fruits in dense clusters from spring through to late autumn, with the strongest flushes a few days after prolonged rain, and can produce successive flushes from the same underground wood for years. Coprinopsis atramentaria is cosmopolitan across the temperate Northern Hemisphere and has been recorded widely in the Southern Hemisphere as well.

As a wood decomposer it attacks buried roots and timber, breaking down cellulose and hemicellulose and contributing to the slow disappearance of stumps and root plates after a tree is felled. The mycelium spreads through the wood and surrounding soil and can persist for many seasons, which is why the same lawn or verge produces tufts in the same spot year after year.

Deliquescence serves the same dispersal function here as in other inkcaps: the gills liquefy progressively so that each band of hymenium sheds its spores and then dissolves away, keeping the remaining surface clear. The dripping ink carries spores onto the ground and onto insects visiting the fruiting bodies, and fungus gnats and flies breed readily in the dissolving tissue.

Shaggy Mane (Coprinus comatus) is taller and narrower, white rather than grey, and covered in coarse upturned shaggy scales; it also grows singly or in loose troops in turf rather than in dense tufts from buried wood. Mica Cap (Coprinellus micaceus) is much smaller and tawny-honey coloured, with a deeply grooved cap dusted with glistening granules when fresh, and it clusters directly at the base of stumps.

Coprinopsis lagopus is more slender and fragile, grey and covered in fine woolly white fibres when young, with a cap that expands, splits and recurves before dissolving. Coprinopsis picacea, the magpie inkcap, is larger, dark brown to blackish with conspicuous white felty veil patches, and grows singly on calcareous woodland soil rather than in tufts.