Fairy Inkcap

Coprinellus disseminatus is the smallest and most gregarious of the common inkcaps. The specific epithet means scattered or sown broadcast, and it describes the habit exactly: rather than a tuft of a dozen fruiting bodies, this species produces sheets of hundreds or even thousands of tiny caps carpeting a stump and the ground around it, appearing overnight after rain.

Its placement has moved repeatedly. It was long known as Coprinus disseminatus and later shuffled between Pseudocoprinus pseudocoprinus and Coprinellus, and it now sits in Coprinellus in the family Psathyrellaceae. Unlike most of its relatives it barely deliquesces at all: the gills blacken and the whole fruiting body collapses and crumbles rather than melting into liquid ink, which is why one of its common names is Trooping Crumble Cap.

Despite its small size it is easy to recognise because nothing else combines such tiny, deeply pleated, pale bonnet-shaped caps with such enormous troop numbers on wood. Individual fruiting bodies last barely a day, and a colony can pass from fresh white to collapsed black within 36 hours.

Cap

0.5-1.5 cm across, oval to thimble-shaped at first, expanding to a bell or bonnet and finally flattening slightly. The colour is whitish to pale cream when very fresh, ageing pale buff, tan or greyish, usually with a warmer ochre or yellow-brown centre, and darkening to grey as the spores ripen. The surface is deeply and regularly pleated or grooved from the margin nearly to the centre, and is covered when young with minute pale hairs visible with a hand lens.

Gills

Widely spaced for the genus, narrow, attached to the stem, white at first, then grey and finally blackish. They do not liquefy into ink; instead the whole cap darkens, collapses and crumbles away.

Stipe

2-4 cm tall and only 1-2 mm thick, white, translucent, hollow, extremely fragile, smooth or minutely downy, with no ring. Stems are usually straight or gently curved and stand densely but individually rather than fusing into tufts at the base.

Flesh & spore print

Flesh almost non-existent, membranous, white, unchanging. Smell negligible. The spore print is blackish-brown to dark brown; spores are smooth, ellipsoid and rather small, with a central germ pore.

Fairy Inkcap is saprotrophic on hardwood and appears in vast troops on and around rotting stumps, on the buried roots of felled or dying broadleaf trees, on fallen logs, and on wood-chip mulch. Willow, poplar, elm, beech, ash and oak are typical substrates. Where the wood is buried, the troops spread across the surrounding lawn or leaf litter in a broad ring or sheet.

Fruiting runs from late spring through autumn, triggered rapidly by rain, and is frequently repeated several times in a season from the same stump. The species is cosmopolitan across temperate regions and is common in woodland, parks, gardens and along street trees. Individual flushes are extremely short-lived, and a colony that is white and crisp at dawn may be grey and collapsing by the following morning.

The mycelium decays dead hardwood, contributing to the breakdown of stumps and root systems and to the return of woody carbon to the soil. Because it fruits so prolifically and so quickly after rain, it is a conspicuous indicator of active decay in a stump or a buried root plate, and its appearance often marks the point at which a felled tree's roots have become thoroughly colonised.

Spore release is achieved without the full autodigestion seen in larger inkcaps. The extremely thin, pleated cap dries and crumbles after a brief spore-shedding period, and the sheer number of fruiting bodies compensates for the small spore output of each one. The soft short-lived fruiting bodies are used heavily by springtails, fungus gnats and small beetles, and the collapsing colonies feed soil invertebrates directly.

Mica Cap (Coprinellus micaceus) is several times larger, tawny to honey-brown, dusted with glistening granules when fresh, and fruits in tight clusters of dozens rather than scattered troops of hundreds. Coprinopsis lagopus is larger again, grey and clothed in conspicuous white woolly fibres, and grows singly or in small numbers.

Parasola plicatilis is a similar size and equally pleated, but grows singly or in small groups in lawns and grassland rather than in troops on wood, and its cap flattens into a thin parasol with a distinct sunken darker disc. Small Mycena species can look superficially alike but have tougher, more elastic cartilaginous stems, non-pleated caps and a white spore print rather than a blackish one.