Panaeolus cyanescens Identification Guide

First Impressions and the Setting

Panaeolus cyanescens is a mushroom of warm pastures. The scene is almost always the same: cattle or horse dung lying in short grass in a humid, warm climate, a day or two after heavy rain, with a scatter of slim mushrooms standing on impossibly thin stalks. From a distance the caps look pale grey or off-white and slightly translucent, and the whole troop has an airy, fragile look. Individual fruit bodies are small, but they often appear in numbers across a single pat and across a whole paddock at once.

The first thing to do is nothing at all: look before touching. This species reacts to handling, and the pattern of staining is far easier to read if you know which parts you touched.

Reading the Cap

The cap is 1.5-4 cm across, hemispherical when very young, then convex, then broadly convex to almost flat with age, sometimes retaining a very low broad umbo. It is thin-fleshed and light, quite unlike the solid dome of the larger dung species.

Colour depends entirely on hydration. Moist young caps are light brown to greyish-brown, sometimes with a slightly darker centre or a narrow darker marginal band. As the cap dries, it pales dramatically to off-white, pale grey or the faintest buff, fading from the centre outward. During that drying it very commonly cracks: the surface splits into fine angular plates or radial fissures, most obviously over the disc. That combination of a pale, dry, cracked surface on a thin cap is highly characteristic.

The margin is even, without veil teeth, and may be faintly translucent when wet. Look along the edge in raking light for a faint bluish or greenish discoloration where the cap has been knocked.

Reading the Gills

The gills are attached by a broad adnate join, close, and moderately broad. Young gills are pale grey; with maturity they take on the classic Panaeolus mottling, a shifting patchwork of grey and blackish that resolves into near black. The gill edges are whitish and finely fringed, visible with a lens and best judged against a mature blackened face.

Handle a gill deliberately with a fingertip and set the cap aside. Damaged gill tissue often develops a bluish-green tinge over the following minutes, a subtler version of the staining seen on the stipe.

Stipe, Base and Colour Change

The stipe is the giveaway on stature: 6-12 cm long but only 1.5-3 mm thick, straight, equal, and often bending slightly under the weight of the cap. It is pale greyish to brownish, conspicuously pruinose over much of its length, hollow, and brittle. There is no ring, though the surface may look finely powdered near the apex. The base is often slightly swollen and can be tinted yellowish or brownish where it enters the dung.

Now the definitive test. Grip the stipe firmly between finger and thumb, or split it lengthways with a blade, and wait. In this species the bruised and cut surfaces stain blue to blue-green, sometimes turning almost teal, and the reaction spreads over several minutes and persists. The base and the lower stipe usually react most strongly. This colour change is the single most useful macroscopic character for separating Panaeolus cyanescens from every other pale dung Panaeolus, all of which stay grey, brown or unchanged. Record its speed and intensity, and check a second fruit body, since very dried-out material can react weakly.

Taking a Spore Print

Cut a mature cap free and lay it gills-down on white paper under a cover for two to three hours. The deposit is jet black, dense and even. Smear a little thin with a fingertip to confirm that there is no brown or purple cast. A brown print rules the species out immediately and points instead at the lawn-dwelling brown-printing genera that share the size and shape.

Substrate, Season and Ecology

This is a strict dung fungus, found on cow and horse dung and on heavily dunged pasture soil, essentially never on wood, litter or bare ground. It is pantropical and subtropical, widespread through the Caribbean, Central and South America, Africa, South and Southeast Asia, Australia and the warmer parts of North America and Europe, and it has spread with cattle-keeping. Fruiting follows warmth plus rain, so in the tropics it can occur year-round while in warm temperate areas it is a mid to late summer species.

Its ecological role is decomposition of the coarse plant residues in herbivore dung. Spores are ingested with grass, pass through the animal, and germinate in the fresh pat, so the fungus tracks grazing animals across the landscape.

Separating the Look-Alikes on Morphology

Panaeolus papilionaceus occurs in the same pastures and has a comparable cap size, but the cap margin is hung with white toothed veil remnants, the cap is greyer and does not crack in the same plated way, and no part of the fruit body stains blue.

Panaeolus antillarum is much larger and stouter, with a thick-fleshed whitish hemisphere on a stiff 4-10 mm stipe, and shows no blue staining.

Panaeolus cinctulus has a browner, more strongly hygrophanous cap with a distinctly darker water-soaked marginal band, a thicker brown stipe, and grows on compost and manured soil as often as on dung. It lacks the plated cracking and does not stain blue-green.

Panaeolina foenisecii is a lawn mushroom with a dark brown, non-mottled to weakly mottled gill face and a dark brown spore print rather than black.

Deconica coprophila shares the dung habitat but has a viscid, reddish-brown, non-cracking cap, evenly coloured gills without strong mottling, and a purple-brown print.

A Compact Field Checklist

Warm-climate dung; thin cap 1.5-4 cm that pales and cracks as it dries; mottled grey-to-black gills with whitish fringed edges; very slender pruinose hollow stipe without a ring; blue to blue-green staining where bruised or cut; jet-black spore print.