Snowy Inkcap Identification Guide

The Setting And The First Look

Snowy Inkcap is a pasture fungus in the most literal sense: it grows on dung. To find it you walk cattle or horse pasture a couple of days after rain and look at cowpats and horse droppings rather than at the ground between them. Well-manured field margins, old muck heaps and the trampled ground around gateways all produce it too.

What catches the eye is a small, brilliantly white, egg-shaped or thimble-shaped cap standing on a slender white stem, looking as though it has been rolled in flour or powdered chalk. Fruit bodies come up singly or in small scattered groups on the same dropping, often over several successive mornings. They are ephemeral - a cap that is a neat white egg at dawn can be a black smear by mid-afternoon - so early morning is the productive time.

Reading The Cap

Size is modest: 1-3 cm tall and about as wide when expanded. The shape sequence is worth learning because it is diagnostic in its own right. The button stage is a small white ellipsoid or cylinder, then it becomes conical to bell-shaped, then the margin flares out and turns upward, and finally the whole cap curls back on itself and dissolves.

The colour beneath the veil is white to very pale grey, but you rarely see it at first because the entire surface is coated in a thick, loose, mealy-floccose universal veil. Under a hand lens this coating looks like a layer of fine white powder or coarse chalk dust, and it rubs off on your fingers. Rain washes it off from the top downward, so an older cap can be white and powdery only around the margin and bare grey over the disc.

As the cap expands, radial grooves develop from the margin inward and deepen until the cap looks pleated. Then the margin blackens and starts to drip.

The Gills And Deliquescence

The gills are crowded, narrow, and free or very narrowly attached to the stem apex. They go through a strict colour sequence: white in the button, then pale grey, then dark grey, then black. The blackening starts at the gill edges nearest the cap margin and moves inward and upward.

Then they autodigest. The gill tissue liquefies into an inky black fluid that drips off the upturned margin, and the process consumes the cap from the rim toward the centre until only a small black-fringed disc is left on top of the stem. This deliquescence is not decay - it is the mushroom's mechanism for releasing spores from a very crowded gill arrangement, and watching it happen over an hour or two is one of the more satisfying things you can do with a hand lens.

Stem, Base And Flesh

The stem is 3-8 cm long and only 1-3 mm thick, white, fragile, hollow, and slightly flexuous. Its surface is finely mealy or floccose from the same veil that coats the cap, becoming smooth and shiny with handling and age. There is no ring. The base is only slightly swollen, sometimes with a small basal disc, and often with white mycelial threads binding the dung.

The flesh is extremely thin - little more than the skin of the cap - white, and unchanging when cut, apart from the black liquefaction of the gills themselves. Odour is negligible.

Taking A Spore Print

You have to be quick, because the cap starts dissolving almost as soon as it expands. Take a cap at the point where the gills have just turned dark grey but the margin has not yet begun to drip, cut the stem off cleanly, and lay the cap gill-side down on white paper under a cover. An hour is often enough.

The print is black. On white paper it may simply look like a wet black stain rather than a dusty deposit, because the liquefying tissue contributes as well as the spores.

Microscopy makes this species easy, and it is worth doing. The spores are strikingly large for such a small mushroom: roughly 14-19 by 10-12 micrometres, blackish-brown in water, and distinctly lemon-shaped, with a broad body drawn out at one end into a short apex bearing a central germ pore. That combination of size and shape is the strongest single character the species has, because several small white dung inkcaps are almost identical to the naked eye.

Substrate, Season And Ecology

The substrate is not merely a preference - it is part of the identification. Snowy Inkcap is coprophilous, living as a saprotroph on herbivore dung, chiefly of cattle and horses, and only rarely on richly manured soil. Its spores pass through the gut of a grazing animal, germinate in the deposited dung, and the mycelium runs through it and fruits within days to weeks.

It fruits whenever the combination of warmth and moisture allows, so in temperate regions that means roughly April to November, with flushes following rain. A single cowpat can produce fruit bodies over a fortnight, and the pat itself is usually a few days to a few weeks old and still soft.

Separating It From Look-alikes By Structure

Coprinopsis cothurnata is the closest match: also white, also veiled, also on dung. It tends to be smaller with a less thickly powdery veil, and its spores are markedly smaller and more ellipsoid than the big lemon-shaped ones here. Microscopy settles it.

Coprinopsis stercorea is tiny, only a few millimetres across, with a granular rather than mealy veil built of rounded cells, and it dissolves almost immediately.

Coprinopsis cinerea grows on compost, straw and manure heaps rather than fresh droppings and is grey-brown with a woolly grey veil, and it is a substantially larger mushroom.

Coprinus sterquilinus is likewise a dung species but is much larger, shaggy rather than powdery, and carries a distinct movable ring on the stem.

Coprinopsis lagopus and relatives grow on woodchip and litter, are grey with a hairy silvery veil, and have far smaller spores.

Egghead Mottlegill (Panaeolus semiovatus) shares the dung habitat and the pale colours, but its cap is smooth, shiny and clay-buff rather than powdery white, it has a ring on the stem, its gills become mottled black-and-grey rather than uniformly black, and critically it never deliquesces.

Conocybe and Bolbitius species on dung have brown, ochre or rusty spore prints, with no blackening or dissolving.

Field Checklist

Small pure white cap thickly coated in powdery veil; grooved margin; free crowded gills passing white to grey to black; cap dissolving into black fluid; slender fragile white hollow stem with no ring; growing directly on herbivore dung; black spore print; very large lemon-shaped spores with a central germ pore.