Panaeolus antillarum Identification Guide

First Impressions and the Setting

Panaeolus antillarum announces itself by size and colour. Where most dung-inhabiting mushrooms are small and drab, this one produces a firm, pale, almost egg-white hemisphere on a long straight stalk, standing clear of the pasture like a golf ball on a tee. You find it on old horse or cattle dung in warm climates: tropical and subtropical pastures, dunged paddocks, and in warm temperate regions the animal enclosures and manured ground where dung sits and weathers.

Note the age of the substrate. This species prefers dung that has already been out in the weather rather than fresh droppings, and it often fruits in loose groups of two to ten on a single pat, days after rain. Because the fruit bodies are tough for the genus, they persist and can be found half-collapsed and sun-bleached long after the flush.

Reading the Cap

The cap is 2-6 cm across and occasionally larger, which is substantial for a dung Panaeolus. It begins hemispherical or bluntly egg-shaped and, crucially, stays that way: it broadens to a wide bell or dome but rarely flattens out and almost never turns up at the rim. If you are looking at a plane, expanded cap, reconsider.

Colour is whitish to pale clay, dirty cream or faintly ochre-buff, sometimes with a slightly warmer tan flush over the very top. The surface is smooth and dry, with a faint sheen, and in dry weather it commonly cracks into a mosaic of shallow, angular plates, particularly over the disc. Some caps develop fine radial wrinkles near the centre. Look hard at the margin: it should be even, without translucent striations and, in typical material, without hanging veil teeth. Absence of a toothed veil fringe is a working character here.

The flesh under the cap skin is white and, for this genus, comparatively thick.

Reading the Gills

Turn the cap over and study the gills at several ages. They are attached to the stipe by a broad adnate join, moderately close, and rather broad. Young gills are pale grey; as the spores ripen they develop the mottled, cloudy, unevenly darkening pattern that defines Panaeolus, looking as though grey and black paint were being stirred together across the gill face. At full maturity they are near black.

Use a lens on the gill edge. It is white and finely fringed, and this pale edge against a blackening face is a good confirmation of the genus.

Stipe, Base and Colour Change

The stipe is long and imposing: 6-15 cm tall and 4-10 mm thick, straight or slightly curved, equal or thickening a little at the base. It is whitish to pale grey-buff, often discolouring dingy brownish towards the bottom with handling and age. The surface is finely longitudinally striate or silky-fibrillose, and the extreme apex is usually pruinose, dusted as if with flour. There is no ring and no ring zone.

The stipe is hollow, with a firm wall that makes it noticeably stiffer than the fragile stems of the smaller dung species. Pull the base free of the dung and check for the coarse white mycelial threads that anchor it.

Now record the colour change, or its absence. Slice the stipe lengthways, bruise the cap margin, squeeze the stipe base, and set the pieces aside for ten minutes. In this species the damaged tissue stays white to greyish or dulls to brownish; it does not develop blue or blue-green tones. Noting a negative reaction explicitly is as much a part of the record as noting a positive one.

Taking a Spore Print

Panaeolus prints beautifully. Cut the cap free, place it gills-down on white paper, cover it and leave it for two to three hours; a ripe cap may deposit visibly in one. The print is jet black, dense and slightly shiny, with no brown or purple undertone when you smear it thin. That black print is the gateway character for the genus and immediately eliminates the brown-printing and purple-brown-printing dung fungi that share the same pat.

Substrate, Season and Ecology

This is an obligate dung decomposer, recorded from horse, cattle and buffalo dung and from heavily manured ground. It is pantropical, common through the Caribbean, Central and South America, tropical Asia, Africa, Australia and warm parts of North America, and it fruits whenever warmth and moisture coincide, which in the tropics can mean any month of the year. In seasonal climates expect it in the hot, wet part of summer.

Ecologically it belongs to the classic dung succession, arriving after the earliest moulds and alongside other coprophilous agarics, breaking down the fibrous residue that grazing animals leave behind. Spores travel by being ingested with herbage and passing through the animal, which is why the fungus appears exactly where the dung falls.

Separating the Look-Alikes

Panaeolus papilionaceus shares the pastures but is smaller and greyer to grey-brown, and its cap margin is hung with distinct white toothed veil fragments. Its stipe is more slender and its cap thinner-fleshed.

Panaeolus semiovatus is the closest match in stature and pale colouring, but it carries a distinct membranous ring on the stipe and has a viscid to sticky cap surface. A ring settles it at a glance.

Panaeolus cyanescens is a much slimmer mushroom with a thin-fleshed cap and, decisively, tissue that stains blue to blue-green where handled or cut.

Stropharia semiglobata grows on the same dung and has a pale yellowish, distinctly slimy hemispherical cap, but it has a ring zone on the stipe and prints purple-brown rather than black.

Coprinopsis species on dung have grooved caps and gills that dissolve into inky fluid.

A Compact Field Checklist

Warm-climate weathered dung; large whitish hemispherical cap that never fully expands and often cracks; no veil teeth on the margin; broad mottled grey-to-black gills with white fringed edges; tall stiff hollow whitish striate stipe with no ring; no blue staining; jet-black spore print.