Turf Mottlegill Identification Guide

The setting and the first impression

You are almost always in grass when you meet the Turf Mottlegill: a well-manured pasture, a paddock, a lawn on rich soil, a grassy track through a farm, or the fertile ground around an old dung pat that has long since crumbled into the sward. The mushrooms come up singly or in loose scattered troops, never in tight clumps, and they are easy to walk past. Each one is small, thin-stemmed and drab, standing 5 to 10 cm tall with a cap no bigger than a large coin.

The impression is of a fragile grey-brown parasol on a wire. It has none of the substance of a Agaricus or the shagginess of an inkcap. What draws the eye, once you know to look for it, is the way the cap changes tone as it dries, and the odd blotchy quality of the gills when you tip the cap over.

Working through the cap

Cap width is typically 1 to 3 cm. The shape starts hemispherical, like a thimble, and opens only as far as broadly convex or bell-shaped. Unlike many grassland mushrooms it rarely flattens out completely and almost never becomes upturned; a mature cap keeps a domed profile.

The surface is smooth and dry to slightly greasy, never sticky and never scaly. It is strongly hygrophanous, and this is the feature to watch. Wet, the cap is a dull grey-brown, mid-brown or dark tan. As it loses water it fades from the centre outwards to pale grey, clay or almost whitish, and while that is happening a distinctly darker band remains around the outer margin. That contrasting rim on a fading cap is one of the most useful field characters in the genus. Sometimes fine, low, radial wrinkles show near the edge; there are no veil fragments hanging from the margin in this species, and no ring on the stem.

Reading the gills

Turn the cap over. The gills are adnate to slightly notched where they meet the stem, moderately spaced, and broad in the middle. Their colour is the whole point of the name. Young gills are pale grey to greyish-brown. As the spores mature, they do so unevenly across the face of each gill, so the surface becomes visibly blotched, marbled or mottled with irregular patches of black on a grey ground. Hold the cap at a low angle to the light and the mottling is obvious. It is not the smooth, even darkening you get in most dark-spored mushrooms.

Look closely at the gill edge with a hand lens. In Panaeolus fimicola the edge is finely fringed and remains whitish, standing out as a pale thread against the blackening face. The gills do not dissolve or deliquesce into ink as an inkcap would; they simply darken and eventually collapse.

Stipe, base and flesh

The stem is 4 to 9 cm long and only 1 to 3 mm thick, straight, hollow, and noticeably brittle: it snaps cleanly rather than bending or peeling into fibres. Colour is greyish-brown to reddish-brown, usually darker toward the base and paler toward the apex, and there is a fine white pruinose bloom in the upper part that rubs off. Some specimens show faint pale longitudinal fibrils.

There is no ring and no volva. The base is simply pinched into the grass, sometimes with a few white mycelial threads binding soil and grass roots. The flesh is thin, watery, grey-brown and unchanging; cut the cap or split the stem lengthwise and nothing flushes blue, red or yellow within the first minutes. Slow, faint darkening at a bruise on the stem base can occur, but there is no rapid or dramatic colour change.

Taking and reading the spore print

Because the spore colour is a hard diagnostic in this group, always print a specimen. Cut the cap free, set it gills-down on white paper or, better, half on white and half on glass or clear plastic, cover it with a cup to keep the air still, and leave it two to four hours. A ripe cap deposits quickly.

The print of Panaeolus fimicola is jet black, sometimes with the faintest brownish cast when thin, but essentially black rather than purple-brown. Smear the deposit with a fingertip and view it against the white sheet: a purple or chocolate tone points elsewhere. Under the microscope the spores are large for so small a mushroom, roughly 11 to 15 by 7 to 10 micrometres, smooth, thick-walled, lemon-shaped to broadly ellipsoid in face view, and each has a conspicuous flat germ pore at the tip. That combination of large, smooth, black, pore-bearing spores confirms the genus.

Substrate, season and ecology

Despite an epithet meaning dung-dwelling, this species is more often a grass-lover than a strict dung specialist. It fruits from rich, manured turf: grazed pasture, paddocks, lawns treated with manure, and the enriched patches that develop around decayed droppings. You may find it beside dung, but usually rooted in the surrounding grass mat rather than directly on the pat itself, which distinguishes its habit from strictly coprophilous relatives.

It is a saprotroph, breaking down nitrogen-rich plant litter and dung residues in the top few centimetres of soil. Fruiting runs from late spring through to late autumn, with strong flushes a few days after rain in mild weather. Because the fruit bodies are short-lived and inconspicuous, the best way to find them is to walk a productive field slowly, looking across the grass at a low angle rather than straight down.

Separating it from its closest look-alikes

Panaeolus papilionaceus (including the forms once called P. sphinctrinus and P. campanulatus) shares the mottled gills and black print but is larger, greyer, and diagnostically fringed: the cap margin carries a row of small, tooth-like white veil fragments, and it typically grows directly on dung.

Panaeolus acuminatus and P. rickenii have narrower, more sharply conical to bluntly pointed caps with a longer, more slender stem, and their caps fade to a reddish or date-brown rather than showing the strong grey tone and dark marginal band.

Panaeolina foenisecii, the common lawn species, is the trap for beginners. It looks similar in size and colour and fruits in the same mown grass, but its spore print is dark red-brown, not black, and its spores under the lens are conspicuously warted and roughened rather than smooth. Its gills darken more evenly and appear mottled only weakly.

Psathyrella species are also fragile grassland or woodland mushrooms with dark spores, but their print is dark purple-brown to almost black-brown rather than pure black, their caps are usually more strongly hygrophanous with a papery, easily split margin, and the gills darken evenly instead of blotching.

Coprinellus and Coprinopsis species may share the habitat and slender build, but their gills eventually liquefy or shrivel into an inky mess, their caps are often furrowed or coated in glistening granules, and the cap flesh is extremely thin and pleated.

Deconica and Agrocybe species in the same fields separate readily: Deconica has a purple-brown print and gills that darken evenly, while Agrocybe species are firmer, thicker-fleshed, usually ringed, and print dull brown.