Dung Roundhead Identification Guide

First Impressions

You find the dung roundhead by looking at the ground in a field rather than at the horizon. Walk a horse paddock, a cattle pasture, a sheep-grazed hillside or a bridleway verge a few days after rain and check the older dung pats. The mushroom that comes up is instantly recognisable in silhouette: a small, shiny, pale yellow half-globe balanced on a stalk that looks far too long and thin for it.

Proportion is the first clue. The cap is 1–4 cm, the stalk can be 12 cm, and the whole thing looks top-light and slightly comical, leaning as it grows toward the light. The second clue is the shine. In damp weather the cap is glossy and genuinely slimy to the touch, and so is much of the stalk, so a picked specimen slides between the fingers and picks up grass seeds and soil grains.

They typically appear as scattered individuals or small groups on a single dung pat, sometimes a dozen at once, each one growing straight out of the substrate.

Reading the Cap

Measure and describe carefully; this is a species where several dull characters together make the identification.

• Size: 1–4 cm, occasionally to 5 cm.
• Shape: hemispherical, and it stays that way. That is the origin of the name: the cap only ever flattens to broadly convex in the oldest specimens and never becomes a plane or upturned disc.
• Colour: pale straw-yellow, buff-ochre or cream, usually a little deeper at the centre and paler toward the rim, fading in sun to nearly white.
• Surface: smooth, strongly viscid to glutinous when moist, drying to a distinct varnished shine. The gelatinous pellicle can often be peeled away from the cap flesh as a transparent film — try this with a knife tip, it is a satisfying confirmation.
• Margin: even, sometimes with a few fine hanging veil fibres in young specimens, not grooved or lined.

Gills

Look under the cap and pay attention to texture as much as colour.

The gills are adnate, broad, and rather widely spaced, ascending from the stipe toward the cap margin so they look tall and deep relative to the small cap. They begin pale grey or clay-buff and darken through violet-grey to dark purple-brown or nearly black-purple.

The important character is that maturing gills develop a mottled, blotchy appearance — uneven patches of dark and light where the spores ripen unevenly across the gill face. Against this, the gill edges usually stay whitish and finely fringed, which shows up well under a lens and against the dark faces.

The Stipe

The stalk is the species' most exaggerated feature: 6–12 cm long but only 2–4 mm thick, straight or gently curved, equal or slightly thickened downward, and hollow.

• Colour: pale straw or whitish, sometimes yellowing toward the base.
• Texture: viscid to glutinous below the ring zone, dry and finely floccose above it. Slide two fingers up the stalk in damp weather and you can feel exactly where the slime stops — that boundary is the veil line.
• Ring: rarely a proper skirt. In most specimens it is a narrow fibrillose band or ring zone, made conspicuous because falling spores stick to the slime there and dye it blackish-purple. A dark band on a pale slimy stalk in the upper third is a strong indicator.
• Base: no volva and no bulb, but there are usually white mycelial strands binding the base into the dung, and often small tufts of white down. Lift the mushroom gently and you will pull up a matted plug of substrate.

Flesh and Colour Change

Cut the mushroom lengthwise. The flesh is thin, soft and whitish to pale yellowish in the cap, more watery and pale in the hollow stalk. It does not change colour on cutting or bruising — no blueing, no reddening, no blackening beyond the ordinary darkening of the maturing gills. There is no milk, and the smell is faint and slightly earthy or of the substrate itself.

The absence of any blue-green staining is worth noting explicitly, because a couple of other roundheads in grassland do develop conspicuous blue-green tones at the stipe base.

Taking a Spore Print

Small, slender, top-heavy caps need a stable set-up.

1. Pick a cap whose gills have gone properly dark.
2. Cut the stipe flush and lay the cap gill-side-down on white paper — a dark print shows best on a pale ground.
3. Cover with a glass or jar to hold the humidity; slimy caps dry fast in wind.
4. Two to six hours is usually plenty; a mature cap can drop a heavy print in under three.

The deposit is dark purple-brown, sometimes described as blackish-purple. Judge the colour where the print is thick and, if you can, compare it side by side with a print from a Panaeolus, which is a colder, sootier black without the violet cast. Microscopically the spores are large, smooth, ellipsoid and have a broad germ pore.

Substrate, Season and Ecology

Protostropharia semiglobata is a coprophilous saprotroph — it lives on and decays herbivore dung. Substrates are:

• horse dung, above all;
• cattle pats;
• sheep, deer and rabbit droppings, on which the fruitbodies are proportionally smaller;
• heavily manured or dung-enriched grassland, where the fungus fruits from soil that has absorbed old dung rather than from a visible pat.

It fruits over a long season, from late spring to late autumn, and in mild regions can appear almost year-round. It responds quickly to rain, and a pat can produce successive flushes over a couple of weeks.

Ecologically it belongs to the dung succession — the ordered sequence of fungi that colonise a pat as it ages. Its spores are taken in with herbage by grazing animals, pass through the gut, and germinate in the deposited dung; the resulting mycelium binds the pat with white cords. The genus is characterised by microscopic spiny cells (acanthocytes) on the mycelium, a feature you can see only in culture or a careful mount of the basal strands.

Separating It From the Look-Alikes

Panaeolus semiovatus. The single most confused species, since it also has a ring and also grows on dung. Separate it by: cap whitish, greyish or pale tan rather than straw-yellow, often becoming wrinkled or cracked on drying; a slightly stouter build; and above all a jet-black spore print against the dung roundhead's purple-brown. Its gills are strongly mottled too, so mottling alone will not settle it — take the print.

Bolbitius titubans. Bright yellow, extremely viscid and equally at home in dunged grass, but it is far more fragile, the cap becomes strongly grooved and quickly collapses, there is no ring at all, and the spore print is rust-ochre.

Deconica coprophila. Also on dung but smaller, with a red-brown to date-brown convex cap, a dry non-glutinous stalk and no ring zone.

Stropharia coronilla. Grows in grass on soil rather than on dung, is much stockier with a short stalk, has a persistent grooved ring on the upper surface, and a yellower cap that is only slightly tacky.

Stropharia caerulea and S. aeruginosa. Distinctly blue-green slimy caps when fresh; no confusion once seen.

Panaeolus papilionaceus. On dung, but has no ring, a darker grey-brown cap, and toothed white veil fragments hanging from the cap margin.

Field Checklist

• Cap 1–4 cm, permanently hemispherical, straw-yellow, glutinous
• Gelatinous pellicle peelable from the cap
• Gills adnate, broad, spaced, mottled purple-black with pale edges
• Stalk very long and thin, slimy below a narrow blackened ring zone
• White mycelial cords binding the base into dung
• Flesh unchanging, no blue-green tones
• Purple-brown spore print
• Herbivore dung or dunged pasture, late spring to late autumn