Petticoat Mottlegill Identification Guide

Where You Will Be Standing

This is a fungus you find by looking at dung rather than at the ground in general. A horse paddock, a cattle pasture, a bridleway margin, an old manure heap that has weathered for a few weeks — anywhere that moist, ageing herbivore dung sits in the open. Petticoat Mottlegill grows straight out of it, usually in small groups, and the first impression is of unusually long, thin, wiry stems holding small grey bells well above the surrounding grass. The stems are so slender relative to the cap that fresh troops seem to hover.

Reading the Cap

The cap is 1–4 cm across and 1.5–3 cm tall, and its shape is a real diagnostic. It begins ovoid, becomes conical, then bell-shaped or parabolic, and it stops there. It does not flatten and it does not develop an upturned margin; even old, weathered fruit bodies keep the campanulate outline with a straight or slightly flaring rim.

Colour is grey-brown, clay, mouse-grey or dull buff, darker over the disc, and strongly hygrophanous — a soaked cap after rain is noticeably darker and slightly translucent, while the same cap in sun pales to a chalky grey-white, often drying from the top down so the margin is briefly darker than the centre. The surface is smooth in the typical form; in the variant many books call var. retirugis it is coarsely wrinkled and net-veined across the disc.

Now look at the margin with a lens, and preferably on a young specimen. Hanging from it you should see a fringe of small, white, triangular tooth-like flaps — the remains of the partial veil. These are the "petticoat" and they are the species' calling card. They are fragile: heavy rain, handling or a few days of weather will strip them, so a veil-less cap does not rule the species out, but a fringed one is strong evidence.

The Gills

The gills are adnate, broad, and only moderately crowded. Their behaviour as they ripen is what gives mottlegills their name. Spores do not mature evenly across the gill face; instead they blacken in irregular patches, so a half-mature gill looks blotched and marbled, pale grey clouded with charcoal, rather than uniformly coloured. Hold the cap so light rakes across the gill surface and the mottling is obvious.

The gill edge is sterile and stays whitish, which under a hand lens shows as a fine pale line running along an otherwise blackening plate. Fully mature gills are near black. There is no liquefaction — the gills dry rather than dissolving into ink.

Stipe, Base and Flesh

The stipe is 6–12 cm and sometimes 15 cm long but only 2–4 mm thick, straight, hollow and rigid, with a slightly brittle snap. Colour is grey-brown to reddish-brown, usually darker toward the base and paler at the apex, where a fine pruinose bloom is often visible with a lens and where fallen spores may dust the surface dark. The whole length is finely fibrous-striate.

There is no ring and no ring zone; the veil goes entirely to the cap margin. There is no volva either, though the extreme base can be slightly swollen and is usually bound to the dung by fine white mycelial threads.

Slice the fruit body lengthways. The flesh is thin, greyish and watery, and it shows no colour change of any kind when cut or bruised — no reddening, no darkening beyond the general drying, nothing. That flat negative result is worth confirming deliberately.

Taking a Spore Print

Cut a mature cap free and set it gills down on white paper, cover it with a glass or cup, and leave it two to four hours; the deposit is often visible within one. The print is black — a genuinely jet, sooty black, not the purple-brown of Psathyrella nor the dark chocolate of Panaeolina.

Under a microscope the spores are large (roughly 13–18 µm long), smooth, thick-walled, very dark, and lemon-shaped in face view, with a broad, obvious germ pore at the apex. That combination of size, shape and pore is characteristic of Panaeolus.

Substrate, Season and Ecology

Petticoat Mottlegill is coprophilous in the strict sense: it fruits on the dung of horses and cattle, less often sheep, deer or other large herbivores, and on heavily manured soil. It is not a grassland litter fungus and it is not found on wood. Season is long — spring through late autumn, and in mild regions almost year-round — with fruiting driven by moisture rather than by date. Dung that has had a week or two to weather and is still damp inside is the productive stage.

The ecology is neat and worth knowing because it explains the habitat. Spores are ingested by grazing animals along with herbage, pass through the gut, and are deposited already primed to germinate on the pat. Dung then supports a predictable succession: fast sugar-consuming moulds first, then small ascomycetes such as Ascobolus and the spore-shooting Pilobolus, and only later the agarics — Panaeolus, Coprinopsis, Deconica and their relatives — which need time to build a mycelium through the pat before fruiting.

Separating It from the Look-Alikes

Panaeolus semiovatus shares the dung habitat but is larger and pale — cream, ochre or dull white — with a smooth, slightly sticky, often wrinkled cap, and, decisively, a genuine membranous ring on the stipe. Petticoat Mottlegill has no ring at all.

Panaeolus acuminatus and P. rickenii are more sharply conical with rich chestnut, strongly hygrophanous caps and a dark marginal band as they dry; they lack the white veil teeth and are more often in rich grass than on the dung itself.

Panaeolus fimicola is smaller and greyer, again with no petticoat fringe, and typically has a narrow darker band at the cap margin.

Panaeolina foenisecii grows on mown lawns and grassy paths rather than dung, has a convex to bluntly bell-shaped cap, mottled gills that end up dull brown, and a dark brown rather than black spore print; its spores are roughened, not smooth.

Psathyrella species can also carry white veil teeth on the margin, but they are markedly more fragile, the cap flesh is thinner and more collapsing, and the spore print is dark purple-brown.

Coprinopsis and Coprinellus species fruit on the same dung with similar grey conical caps, but their gills deliquesce into black ink, and the cap surface is often pleated or dusted with granular veil.

A Quick Field Sequence

Dung substrate; long slim stem; permanently bell-shaped grey-brown hygrophanous cap; white triangular veil teeth on the margin; broad adnate gills mottled black in patches with a pale sterile edge; no ring, no volva, no colour change; jet-black spore print with large lemon-shaped spores.