Snowy Inkcap

The Snowy Inkcap, Coprinopsis nivea, is unmistakable at first glance among dung fungi: a small, egg-shaped cap of the purest white, looking as if it has been rolled in flour or dusted with chalk. The coating is a thick, mealy universal veil that rubs off at a touch, leaving a smoky grey pleated cap beneath.

It is a specialist of herbivore dung, one of a large community of fungi that fruit in sequence on a single cowpat over weeks or months. Within that community the inkcaps are the conspicuous large-fruiting stage, appearing after the tiny early ascomycetes and the pin moulds have already come and gone.

Like its relatives, the species pairs a very short-lived fruit body with a rapid, decisive method of spore release: as the gills mature they liquefy from the cap edge inwards, and the black droplets carry away spores that had a moment before been packed on the gill faces. Under the microscope C. nivea is notable for spores that are among the largest in the genus, distinctly lemon-shaped and jet black.

Cap

Small, 1–3 cm tall and across when expanded. Young caps are narrowly egg-shaped to cylindrical, then conical or bell-shaped, finally flattening and splitting at the margin. The whole surface is coated in a thick, loose, floury to mealy pure white veil that is easily brushed away, revealing a pale grey, deeply and finely grooved surface beneath. In age the margin turns black and curls as it dissolves.

Gills

Free from the stipe, crowded and very narrow. They are white when young, quickly turning grey, then purplish black, and then deliquescing into black liquid from the cap margin upward, so that the cap dissolves itself away over a few hours.

Stipe

Slender and fragile, 4–10 cm long and only 1–4 mm thick, hollow, white throughout, and dusted with the same white mealy veil particles, especially toward the base, which is slightly swollen and often rooted into the dung. There is no ring.

Flesh and spore print

The flesh is extremely thin, white, and watery, without notable odour. The spore print is black. Microscopically the spores are unusually large, thick-walled, and lemon-shaped with a distinct apical pore — a strong confirming character for the species.

Almost exclusively found on the dung of large herbivores, above all cow and horse droppings in pasture, and also on dung heaps, manured ground, and richly manured garden beds. It typically appears on pats that are a few days to a few weeks old and still moist, and often fruits in company with other dung specialists.

The season is long, running from spring through to late autumn wherever rain keeps the substrate damp, and fruiting can occur in mild winter spells. It is cosmopolitan, recorded throughout Europe, North America, Australasia, and elsewhere alongside grazing livestock. Fruit bodies come up singly or in small scattered groups on the surface of a pat, usually overnight, and are gone within a day.

Coprinopsis nivea is a coprophilous saprotroph — a dung decomposer. Its spores are ingested by grazing livestock along with grass, pass through the gut where heat and digestive chemistry break spore dormancy, and germinate in the deposited dung. This is the classic dung fungus life cycle, and it explains why the species is so tightly bound to grazed pasture.

Once established, the mycelium exploits the partly digested plant fibre in the pat, competing with a crowded succession of bacteria, moulds, and other fungi. Fruiting fast, releasing spores as an inky liquid, and finishing within a day is a way of getting ahead in that competition. The spores must ultimately be returned to grass leaves to be ingested once more, so many dung fungi are adapted to project or spread spores away from the pat, which livestock avoid cropping.

Coprinopsis cothurnata is another small whitish dung inkcap, but its veil is finer and more granular than mealy and it often shows a slightly ochre-tinted disc. Coprinopsis stercorea is smaller still, with a more granular-crystalline veil, and is separated with certainty only by microscopy of the veil cells.

Coprinopsis lagopus also has a white veil but it is fibrous and woolly rather than powdery, the mushroom is far larger, and it grows on woodchip and litter rather than dung. The Common Inkcap (Coprinopsis atramentaria) is much bigger, has a bald ochre-grey cap without a white coating, and clusters from buried wood rather than fruiting on pats.