Egghead Mottlegill

The Egghead Mottlegill (Panaeolus semiovatus, sometimes placed in Anellaria) is the largest and most conspicuous of the dung-inhabiting mottlegills. Where most Panaeolus are small, dark and ringless, this species is comparatively tall, pale clay to almost white, and carries a genuine membranous ring — the feature that prompted its former placement in a separate genus.

The cap holds a semi-ovoid or egg-shaped profile for a long time, only slowly becoming broadly bell-shaped, and never opens flat. When wet the surface is smooth, greasy and slightly shining; as it dries it often becomes finely wrinkled and lacquered-looking, catching the light in a way that makes it easy to spot on a dung pat from several metres away.

Like the rest of the genus, its gills mature unevenly, producing the mottled or clouded appearance from which mottlegills take their name. The spore deposit is jet black and readily stains the ring, which is often dusted dark by fallen spores from the gills above it.

Cap

2 to 6 cm across, semi-ovoid or egg-shaped, becoming broadly conical to bell-shaped but never flattening. The surface is pale clay, whitish-ochre or pale tan, darker at the apex, smooth and greasy to slightly viscid when moist, and frequently drying with a fine network of wrinkles and a shining lacquered look.

Gills

Adnate, broad and crowded, pale grey at first and maturing through mottled grey-black to almost black. The mottled, clouded pattern is caused by uneven spore ripening. Gill edges stay whitish and finely fringed.

Stipe

Tall and slender, 6 to 15 cm high and 3 to 8 mm thick, cylindrical or slightly swollen at the base, whitish to pale straw, finely powdery or striate above the ring. A distinct membranous ring sits in the upper half and is usually blackened by fallen spores. There is no volva.

Flesh & spore print

The flesh is thin, pale and unchanging when cut. Odour is not distinctive. The spore print is jet black, and the spores are smooth, thick-walled, lemon-shaped and have a broad germ pore.

This species is coprophilous, growing directly on the dung of large herbivores. Horse dung is by far its most frequent substrate, but it also occurs on cow pats and on well-rotted manure heaps and manured field edges. Fruitbodies stand singly or in small groups directly on the pat, often with the stipe base gripping the fibrous surface.

It has a long season, appearing from spring through to late autumn whenever fresh dung and warm damp conditions coincide, and is often among the first agarics of the year on pasture. The species is widespread and common across Europe, North America and temperate Asia, following grazing livestock wherever they occur.

Panaeolus semiovatus is a specialised dung decomposer. Its spores are taken up by grazing animals along with herbage, pass unharmed through the digestive tract, and germinate in the deposited dung, where they exploit an exceptionally nutrient-rich but short-lived and highly competitive substrate. Thick-walled, dark, heat- and acid-resistant spores are an adaptation to this passage.

Succession on a dung pat is rapid and orderly, with fast-growing moulds and small ascomycetes appearing first, followed by Coprinopsis species and mottlegills. To rejoin the cycle, spores must land on nearby grass and be ingested once more, so the tall stipe of this species helps lift the cap clear of the pat and improve the chances of spores reaching surrounding vegetation.

Panaeolus papilionaceus grows in the same habitat but is darker grey-brown, smaller, has no ring at all, and typically shows a fringe of white toothy veil fragments hanging from the cap margin. Other Panaeolus on dung are smaller and ringless.

Protostropharia semiglobata, the Dung Roundhead, is the most confusing companion: it too has a ring on a long slender stipe, but its cap is a distinctly rounded hemisphere, bright yellow-ochre and markedly viscid, and its spore print is purple-brown rather than black. Stropharia species generally have purple-brown prints and evenly coloured gills. Bolbitius species on dung are far more fragile with rusty-brown prints and quickly collapsing caps, and Coprinopsis species on the same pats deliquesce into ink.