Egghead Mottlegill Identification Guide

The First Impression and the Setting

The habitat comes first. You are in a horse paddock, a cattle pasture, a deer park, a manured field edge or a well-used bridleway, and you are examining droppings rather than turf. What you notice is a surprisingly tall, stiff, clean-looking mushroom standing 8 to 15 cm high above the grass, with a smooth pale cap shaped like the end of an egg.

The paleness is what draws the eye. Most dung fungi are drab greys and browns; this one is ivory, cream or pale clay and looks almost polished in wet weather. It grows straight out of the dropping, singly or in small troops, occasionally with half a dozen from one pat, and it holds itself upright on a stalk that is noticeably stiff for its thickness.

Reading the Cap

The cap is 2 to 6 cm, occasionally 8, and its shape is a primary character: ovate, bluntly conical or bell-shaped, and it never expands flat. Even the oldest fruitbody keeps a domed egg profile with a straight or slightly flaring margin. If you are holding something with a fully opened, plane cap, look again at the genus.

Colour is whitish, ivory, cream, pale clay or a warm buff, usually a shade deeper over the crown. The surface is smooth and, in humid weather, slightly greasy or subviscid, so it shines and picks up grass seed.

As it dries the cuticle contracts and produces the feature that names the species in the field for many people: a fine network of cracks and shallow wrinkles beginning at the top and spreading down, so an old cap acquires a mosaic or hide-like texture. Young caps may carry small white veil fragments hanging at the margin. The margin is not grooved or striate.

Reading the Gills

Turn it over and study a gill face against the light. The gills are adnate, broad, and moderately crowded, and the important thing is how they change colour.

They begin pale grey to clay, then develop irregular dark patches and marbling, and finally become almost uniformly blackish-brown. The intermediate blotched stage is the diagnostic one: because spores in a given patch of a gill mature together, the surface becomes piebald, mottled with black on a paler ground rather than colouring evenly. This is the character that names the genus, and it should be obvious on any mature specimen.

Under a hand lens the gill edges remain finely white-fringed, a pale line contrasting with the darkening face.

The Stipe and Ring

The stalk is 6 to 15 cm long, occasionally 20, and 3 to 8 mm thick, straight, stiff and slightly tapered upwards. It is whitish to pale cream, dulling to a brownish tone at the base, finely powdery near the apex and finely fibrous lower down, with faint longitudinal striations. The base is a little swollen and set firmly into the dung, with white mycelial threads running through the substrate.

The ring is the character that finishes the identification. There is a distinct membranous collar, usually around the middle of the stalk or a little higher, which flares outwards, often collapses back against the stem, and is quickly stained blackish-brown by spores falling onto it from above. In older or weather-beaten material it can be reduced to a torn band or a dark line, so look carefully before concluding it is absent.

This is essentially the only commonly encountered mottlegill with a proper membranous ring, so finding one narrows the field dramatically.

Flesh and Colour Change

Split the fruitbody lengthwise. The cap flesh is thin and whitish; the stalk is hollow or has a narrow central channel and is fibrous enough that it breaks with a stringy, splitting fracture rather than a clean snap.

Nothing changes colour. The cut surfaces stay whitish, handling produces no stain, and bruising the cap leaves no mark beyond a slight discolouration where the cuticle is damaged. Record that lack of reaction deliberately, because several of the fungi you are sorting it from also show none, and only the combination of characters resolves the group.

Taking a Spore Print

Trim the stalk flush, set the cap gills-down on white paper, cover it and give it two to four hours. The deposit is jet black, sometimes with a bluish cast, and it is dense enough to be unmistakable.

Under a lens the spores are large - roughly 14 to 20 by 8 to 11 micrometres - smooth, thick-walled, opaque dark brown to black, lemon-shaped in face view, and finished with a broad truncate germ pore at the tip. A jet-black print, plus a membranous ring, plus dung as substrate, is an extremely tight combination.

Substrate and Season

The species is strictly coprophilous. Horse dung is the classic substrate, cattle dung is frequent, and sheep, deer and other grazers produce it less often. It favours well-formed, nutrient-rich droppings and typically appears a few days to a couple of weeks after deposition, while the pat is still intact rather than crumbling. Straw-based manure heaps and ground dressed with manure also produce it.

The season runs from spring to late autumn with peaks after warm wet spells, and in mild oceanic climates fruitbodies turn up in most months. Individual fruitbodies are short-lived: the cap wrinkles, cracks and collapses within a few days, so a single pat often produces several successive flushes over a couple of weeks.

Ecologically it belongs to the dung succession, arriving after the fastest-moving moulds and small ascomycetes and alongside the other larger dung agarics. Spores travel by being consumed with herbage and passing through a grazing animal, which is why the fungus is so tied to pasture.

Separating It From the Look-alikes

Dung Roundhead, Protostropharia semiglobata. The commonest confusion, sharing the substrate, the long stalk and a veil. Its cap is a low, smooth, glossy, pale straw-yellow hemisphere that stays domed and does not crack into a mosaic; its gills darken fairly evenly to purple-brown with little mottling; its veil forms a slimy dark band rather than a flaring membrane; its lower stalk is viscid in wet weather; and its spore print is purple-brown, not black.

Panaeolus papilionaceus and its relatives. Also on dung and also mottled-gilled, but with no ring at all, a greyer or browner and often more conical cap, and small white toothed veil fragments hanging from the young margin. Slimmer and generally smaller.

Panaeolus antillarum. A large pale dung species whose cap also cracks in dry weather, so it looks close. It lacks a ring, which is the quickest separation.

Panaeolus fimicola and Panaeolus acuminatus. Smaller, darker, with caps that fade markedly as they dry, and again ringless.

Agrocybe pediades and Bolbitius species. Common on manured ground rather than on the dropping itself. Their spore prints are rusty to cinnamon-brown and their gills colour evenly rather than becoming blotched.

Stropharia coronilla. Grassland rather than dung, a shorter stouter stalk, a dry deeper yellow cap, a grooved membranous ring and a purple-brown print.

Coprinopsis species on dung. Numerous and often superficially similar in stature, but their gills dissolve into black ink as they mature and the whole fruitbody collapses, and most have shaggy, fibrillose or granular cap surfaces.

A Working Sequence

Confirm the substrate is dung. Check for a persistently egg-shaped pale cap that cracks as it dries. Look at a gill face for blotchy, uneven blackening with a white edge. Find the membranous ring, or the dark band it leaves behind. Take a print and confirm it is jet black. Those five steps, in that order, will place almost every collection.