Dung Roundhead

The Dung Roundhead (Protostropharia semiglobata, long known as Stropharia semiglobata) is one of the most familiar dung-inhabiting gilled fungi of pasture and rough grassland. Its shape is the giveaway: the cap holds a strikingly regular half-sphere long after most mushrooms have flattened out, and it is perched on a disproportionately long, thin, straight stem that lifts it clear of the dung pat.

The genus Protostropharia was split from Stropharia to accommodate a small group of dung specialists that share purple-black spores, a glutinous cap and characteristic microscopic features, including the astrocystidia found on the basal mycelium. Family placement is in the Strophariaceae, alongside the roundheads, scalycaps and brownfin fungi.

It is a common and widely distributed species that can be found for much of the year wherever livestock graze. Its combination of pale straw colouring, sticky cap, blackening gills and a fugitive slimy ring zone on the stem makes it one of the easier dung fungi to recognise without a microscope.

Cap

The cap is 1–4 cm across and remains hemispherical or bluntly conical for a long time, only occasionally expanding to broadly convex in age. The colour is pale straw-yellow, buff or clay, sometimes almost whitish, and typically a little deeper toward the centre. When moist the surface is markedly viscid to glutinous and shines; in dry weather it becomes tacky and then merely smooth and matt. The margin is even and not striate.

Gills

The gills are broadly adnate or slightly adnexed, fairly broad and rather widely spaced. They begin pale grey or clay-coloured and darken through mottled purplish-grey to almost black as the spores mature — the uneven, blotchy darkening is characteristic. The gill edges usually remain paler and whitish, giving a fine contrasting line.

Stipe

The stipe is conspicuously long relative to the cap, typically 4–12 cm tall but only 2–4 mm thick, straight or slightly wavy, and often slightly enlarged at the very base. It is whitish to pale yellow, smooth above and often glutinous or sticky below in wet conditions. A thin, glutinous, dark-dusted ring zone is present in young specimens where the veil breaks; it is easily washed away, and in older material only a darkened band of trapped spores marks its position. Fine white mycelial strands frequently run into the substrate at the base.

Flesh & spore print

The flesh is thin, whitish to pale yellowish, and does not change colour when cut or bruised. The spore print is dark purple-brown to purple-black.

This species is a dung specialist, fruiting directly on the droppings of herbivores — most commonly horse and cow dung, but also sheep, deer and other grazing animals — and on well-manured ground and old dung-enriched straw. It is a mushroom of pastures, paddocks, upland sheepwalk, grazed woodland rides and other open grassland, and rarely strays far from the substrate that supports it.

Fruiting is possible from spring right through to late autumn and even into mild winters, with the strongest flushes after rain. The species is widespread and common across Europe and North America and has followed grazing livestock to many other parts of the world, making it effectively cosmopolitan in temperate agricultural landscapes.

Protostropharia semiglobata is a coprophilous saprotroph: it decomposes dung and the partly digested plant fibre it contains. Spores are thought to be dispersed onto surrounding vegetation and swallowed by grazing animals, passing through the gut and being deposited in fresh dung where germination follows — a life cycle shared with many dung fungi and one reason the species tracks livestock so closely.

Within the dung community it is a relatively late arriver, following the fast-fruiting moulds, Pilobolus and small ascomycetes, and helping break down the tougher fibrous remnants of the pat. The long stem is an adaptation to this habitat, raising the cap above the moist, crusting dung surface so that spores can be caught by moving air.

Panaeolus semiovatus (the Egghead Mottlegill) shares dung pats and also has a hemispherical, shiny cap and a stem ring, but its cap is smoother, whiter and more leathery-wrinkled when dry, its gills are strongly mottled grey and black, and its spore print is jet black rather than purple-black. Deconica coprophila is smaller and darker, with a reddish- to date-brown cap and no ring on the stem.

Stropharia coronilla grows in grassland rather than on dung, has a shorter, stouter stem and a well-developed persistent ring with fine striations on its upper surface. Bolbitius titubans, the Yellow Fieldcap, may share manured grassland and is also sticky and yellow, but its cap is fragile, deeply grooved and quickly collapsing, and its spore print is rusty ochre rather than purple-black. Agrocybe species on manured ground have brown spore prints and dry, cracked caps.