Blue Edge Pinkgill Identification Guide

The setting and the first impression

The Blue Edge Pinkgill is a grassland fungus, and the habitat does a lot of the identification work before you have picked anything. You will usually be walking short, unimproved turf in late summer or autumn: an old churchyard, a mossy lawn that has never been fertilised, a coastal dune slack, a heathy sheep pasture, or the kind of hillside grassland where waxcaps and earthtongues come up in the same square metre. Against that pale, mossy background the fungus reads as a small dark button, blue-black to slate-blue, standing on a thin dark stem 3-6 cm tall. It is easy to lose against a dark patch of moss and easy to mistake for a wet twig. Once your eye has locked onto one, you nearly always find several more in the same few metres, sometimes scattered singly, sometimes in loose groups.

Reading the cap

Pick one and look at the cap first. It is small, roughly 1-3.5 cm across, and its profile changes with age: convex at first, then flattening, and almost always developing a depressed centre, so a mature cap looks like a shallow dish with a distinct navel. The colour is a dark, cool blue-black or blue-grey, often close to the colour of wet slate, and it fades unevenly to a browner grey as the cap dries out, so a single group can show several shades at once. The surface is not smooth: under a lens the centre is finely fibrillose to minutely scaly, with the scales darkest at the very middle and radiating fibrils running outwards. When wet the cap is hygrophanous and slightly translucent at the margin, so the lines of the gills beneath show through as faint radial striations. In dry weather that striation disappears and the cap looks matt.

The gills, and the character that names the species

Turn the cap over. The gills are moderately spaced, fairly broad, and attached to the stem with a notch or a short decurrent tooth rather than running far down it. Their colour is the standard pinkgill sequence: pale grey to whitish-grey while young, then progressively flushed salmon to dull pink as the spores ripen, so an old cap has clearly pink gills even though the cap above is blue-black. Now bring a hand lens right down onto the gill edge. In Entoloma serrulatum the edge is finely toothed or serrated and stained a dark blue-black that contrasts sharply with the pale pink gill face. Held to the light and viewed edge-on, a mature gill looks as if someone has run a fine dark pen along its rim. That dark, minutely toothed edge is the single most diagnostic field character the species has, and it comes from a fringe of dark, clustered cells on the margin. Check several gills on more than one cap, because a very young or very weathered specimen can show it only faintly.

Stem, base and flesh

The stem is slender, 3-6 cm long and only 2-4 mm thick, more or less equal along its length, sometimes flattened or slightly grooved, and often a little curved where it leaves the turf. Its colour matches the cap, dark blue to blue-black, usually a shade paler and more polished than the cap, and the extreme apex is finely pruinose under a lens. It is hollow or narrowly stuffed rather than solid, and it snaps cleanly rather than tearing into long fibres. Ease the whole fruit body out of the turf rather than pinching the stem off, because the base carries useful information: there is a small tuft of white mycelium binding soil and moss fragments, and that white base against the blue-black stem is a good confirmatory detail. The flesh throughout is thin and greyish-blue, and it does not change colour when cut or bruised.

Taking a spore print

The spore print settles the genus and is worth doing on any small dark grassland agaric. Cut the stem flush with the gills, set the cap gills-down on white paper or on a glass slide, cover it to hold moisture, and leave it two to four hours; small caps release spores quickly. The deposit is pink to salmon-pink, sometimes reading as brownish-pink in a thick print, and against white paper it is unmistakable. If you have a microscope, the spores are the clincher for the genus as a whole: they are distinctly angular in outline with five to eight straight facets, roughly 8-11 by 6-8 micrometres, and they look like small irregular crystals rather than smooth ellipsoids. No other group of small dark grassland agarics combines a pink deposit with angular spores.

Substrate, season and ecology

Entoloma serrulatum grows on soil, not on wood, and it is a species of nutrient-poor, undisturbed short turf. Mossy lawns, old grazed pasture, dune grassland, heath edges, upland flushes and the mossy margins of woodland rides all suit it, and it often shares ground with waxcaps, clubs and other indicators of long-unimproved grassland. It fruits from midsummer to late autumn, peaking after the first sustained autumn rains. Its precise trophic role is still argued over, but it behaves as a soil fungus of stable, low-fertility swards rather than a wood decayer, and its presence is generally taken as a sign that the ground has escaped fertiliser and ploughing for a long time.

Separating it from look-alikes on morphology alone

The blue-black grassland pinkgills form a difficult cluster, so work through them deliberately.

Entoloma chalybaeum is the closest match in size, colour and habitat, and the two grow together. The separation is the gill edge: in E. chalybaeum the edge is concolorous with the gill face, so there is no dark line and no obvious serration under a lens. Its cap also tends to be more evenly fibrillose and less deeply depressed.

Entoloma nitidum is a taller, more slender, steel-blue species that grows in damp woodland and on mossy woodland floors rather than in open turf, has a smooth, shining, non-scaly cap, and lacks the toothed dark gill edge.

Entoloma corvinum is darker still, almost black-blue, with a more conical to convex cap, whitish gills that flush pink only late, and no dark edge.

Entoloma asprellum shares the blue-grey tones but has a more strongly striate, sometimes almost translucent cap and paler gill edges.

Small blue Mycena species occasionally confuse the eye at a distance, but they have white spore prints, gills that never turn pink, and a much more fragile, waxy stem that exudes no white basal tuft.

Blue-tinged Cortinarius species in acid grassland are stouter, carry cobwebby veil remnants on the young stem, and produce a rusty-brown spore print that could not be mistaken for salmon-pink.

Field checklist

Short unimproved turf, cap 1-3.5 cm and blue-black with a depressed navel, finely fibrillose centre, gills grey then salmon-pink with a dark, minutely toothed edge under a lens, slender blue-black hollow stem with white basal mycelium, pink spore print, angular spores. Habitat plus gill edge is the combination that carries the identification.