Mousepee Pinkgill Identification Guide

The Setting

This is a fungus of old, short, unimproved grassland on lime-rich ground. Chalk downland, limestone pasture, ancient churchyards, dune slacks, montane turf and long-established lawns that have never been fertilised are all typical. It also strays into open, grassy glades and path edges in calcareous woodland. It belongs to the classic waxcap grassland community, so it turns up alongside Hygrocybe and Gliophorus species, earthtongues, fairy clubs and other pinkgills, and a site producing it is worth a full grassland survey. Fruiting runs from summer into late autumn, usually a week or so after steady rain.

First Impression

What stops you is the colour. A genuinely green mushroom is rare in turf, and this one is small, slender and green from top to bottom. Typically you see a 1 to 3 cm cap on a thin, brighter yellow-green stem, half hidden between grass blades, sometimes singly and sometimes in loose scatterings across a few square metres. Get on your knees for it, because at standing height it disappears into the sward.

Reading the Cap

The cap is 1 to 4 cm across, convex at first and soon flattening, and it develops a distinct central navel or depression, sometimes deep enough to look like a small funnel. The margin is translucent-striate when moist, so you can see the lines of the gills through the cap skin, and it often becomes slightly wavy or lobed with age.

The surface is finely fibrillose and may become minutely scaly at the centre. Colour is olive-green to yellow-green, often browner or darker over the disc, sometimes with brownish-olive tones towards the margin. It is hygrophanous, so as it dries it fades from the centre outwards to a paler, yellower or buff-green tone, and a dried-out specimen can look much duller than the guidebook picture.

Reading the Gills

Gills are adnate, frequently with a short decurrent tooth running down the stem, moderately spaced, and rather broad and ventricose, so they look deep for such a small cap. Their colour changes with maturity, and the sequence is a key part of the identification. They start whitish to pale greenish-yellow, take on a pinkish tinge as spores develop, and finish a clear pink to pinkish-brown. The gill edges are even and concolorous. Damaged gills often develop blue-green stains at the point of injury.

Reading the Stipe

The stipe is 2 to 5 cm long and only 1 to 4 mm thick, cylindrical, smooth, hollow, and quite often flattened or shallowly grooved along its length. Its colour is a brighter, more saturated yellow-green or grass-green than the cap, and this contrast is a useful early clue.

Then do the definitive field test. Grip the stem between finger and thumb and rub it gently, or simply pick the fruit body and set it in a collecting box for a few minutes. The handled area stains a strong blue-green to turquoise, and old or bruised specimens can be almost entirely blue-green over the lower stem. Cut surfaces do the same. At the very base there is a small tuft of white mycelial down binding soil and grass roots.

Flesh and Odour

The flesh is very thin and greenish, and it discolours blue-green where cut. Crush a fragment between your fingers and a sharp, ammoniacal smell is released, commonly described as mouse urine, which is exactly what the English name records. Odour is a legitimate morphological character here and it is reliable in fresh material, though it fades in old and dried specimens.

Taking and Reading a Spore Print

Use white paper rather than dark card, because a pink deposit shows poorly on black. Cut the cap free and lay it gills down under a cover for two to six hours. A mature cap gives a pink to pinkish-brown deposit; a very young one may give nothing.

If you have a microscope, the spores clinch the genus. Entoloma spores are angular in outline, essentially little polyhedra, with five to seven distinct facets, and in this species they measure roughly 10 to 14 by 8 to 10 µm and are close to isodiametric. No other grassland genus with a pink print has spores shaped like this.

Substrate and Season

The fungus grows from soil in closed, mossy, short turf. It is not associated with wood, dung or leaf litter, and it does not appear on improved, heavily fertilised grassland. Late summer through autumn is the core season, extending into early winter in mild coastal areas.

Separating It From Look-alikes

Entoloma chalybaeum, E. serrulatum and E. nitidum are the other small, dark, striking pinkgills of the same grasslands, but they are blue, blue-black or steel-blue rather than green, and although they can bruise darker they do not develop the same turquoise staining from a green ground colour.

Entoloma corvinum has a blackish-blue cap with a paler, often whitish stem, again lacking the green tone.

Gliophorus psittacinus, the parrot waxcap, is the commonest field confusion because it is also small and green in the same turf. It is separated instantly by its thick, glutinous, slimy coating over both cap and stem, its thick waxy gills, its habit of shifting through yellow, orange and pink as it ages, and above all its white spore print.

Hygrocybe citrinovirens is larger, yellow-green, dry and fibrillose, but has waxy gills and a white spore print.

Stropharia aeruginosa is blue-green but has a viscid cap with whitish scales at the margin, a distinct ring on the stem, a purple-brown spore print, and grows in woodland, wood chip or rich grass rather than fine old turf.

In practice, the three-part combination of a green umbilicate cap, a stem that stains turquoise where you touch it, and a pink spore print is unique among grassland fungi.