Sky Blue Mushroom Identification Guide

The first impression

Nothing else on the forest floor looks like this. You are walking a shaded track in damp native forest, the ground deep in leaf litter and moss under tawa, rimu, beech or tree ferns, and among the browns there is a small, intensely blue cone standing about five centimetres high. The colour is not a pale wash but a saturated indigo to turquoise, brightest on a young specimen and slowly draining towards a duller blue-green or greyish blue as the mushroom ages and dries. Sky Blue Mushroom is generally solitary or in small scattered groups, always on the ground rather than on wood, and it is fragile enough that a careless hand will crumple the cap. Its silhouette is as diagnostic as its colour: a sharply conical cap drawn up into a pointed central peak, sitting on a slender stalk of the same blue.

Reading the cap

The cap is small, roughly one to four centimetres wide and often taller than it is broad in youth. It begins conical or bell-shaped, expands only slightly, and retains a prominent, sharply pointed umbo at the apex. The margin is usually inrolled at first, then straight, and often splits radially as the mushroom dries. Surface texture is important: it is dry, minutely fibrillose to finely scaly in radiating lines, the fibrils running from the peak to the rim and giving a subtly streaked appearance rather than a smooth, glossy skin. Colour is deep blue to indigo, sometimes with a greenish or violet cast, generally darkest at the summit. Note that the blue is not a bruising reaction: it is the resting colour of the tissue, present from the button stage, and it fades rather than intensifies with handling.

The gills

The gills carry the clock of the identification. Young specimens have gills that are blue or bluish-white and fairly close together. As the spores ripen, a pink or salmon flush spreads through them until a mature cap shows gills that are pinkish with blue edges or blue-tinged faces, a two-tone effect that is one of the loveliest things in the genus. Attachment is adnate to slightly emarginate, the gills meeting the stipe squarely or with a small notch, sometimes with a short decurrent tooth. They are moderately broad and ventricose, and the edges are even. There is no partial veil, so there is never a ring or a cortina and never a fringe of veil fragments on the cap edge.

Stipe, base and flesh

The stipe is two to seven centimetres tall and only two to five millimetres thick, more or less cylindrical or slightly widened towards the base, and hollow or stuffed in the centre. It is the same blue as the cap, sometimes brighter, and it is covered with fine longitudinal fibrils that catch the light. The base bears a small tuft of white or pale blue mycelium binding fragments of leaf and moss; lift it out with a fingertip of soil so this is not lost. Cut the mushroom in half and the flesh is thin, pale blue to bluish-white and unchanging on exposure; there is no reddening, no darkening and no milk. The odour is faint, at most slightly earthy, and is not a useful character here.

Taking a spore print

The blue colour is so distracting that people forget the print, but it is what proves the genus. Set a mature cap gills-down on white paper, cover it to hold humidity, and leave it several hours. The deposit is pink to salmon or pinkish-brown, exactly as in every other pinkgill, and the contrast between a blue mushroom and a pink print is the definitive combination. Under a microscope the spores are angular in profile, with five to seven corners, and roughly as broad as they are long, matching the rest of the genus and instantly separating it from any smooth-spored blue mushroom.

Substrate, season and setting

Sky Blue Mushroom is a litter fungus of moist native forest, best known from New Zealand, where it is a celebrated emblem and has appeared on both a postage stamp and the fifty dollar note; closely comparable blue pinkgills have been reported from other parts of Australasia and Asia. It grows from soil, humus, moss and rotting leaf debris in shaded, humid, high-rainfall forest, often near the base of broadleaf trees and among ferns along stream banks and track edges. Fruiting is concentrated in the wetter months of autumn and winter, and specimens are far more frequent after prolonged rain. It is not a wood-inhabiting species and it is not found in open pasture.

Separating it from look-alikes on morphology alone

Blue mushrooms are rare, but there are a few, and the separations are clean.

Pixie Parasol, Mycena interrupta, is the most likely confusion at a glance. It is much smaller, only a centimetre or so across, with a smooth, sticky, hemispherical to convex cap that is pale sky blue and translucently striate, and it grows in clusters on rotting wood, never on soil. Its stipe rises from a distinct white basal disc, its gills are white to pale blue, and it drops a white spore print.

Some waxcaps in the genera Gliophorus and Hygrocybe carry blue-green tones. They are separated by texture: their caps and stipes are glutinous and slippery, their gills are thick, waxy, widely spaced and often decurrent, and their prints are white. Sky Blue Mushroom is dry and fibrillose with close, notched, pink-ripening gills.

Among the cortinarias, Cortinarius rotundisporus and similar blue-capped species have a cobwebby cortina between cap margin and stipe in youth, leave a rusty fibrillose zone on the stalk, and drop a rust-brown print, plus their caps are usually viscid and more domed than sharply conical.

Other blue-toned Entoloma species exist in the same forests, and here the details matter: they differ in the sharpness of the umbo, the intensity and hue of the blue, the degree of cap scaliness, and the extent to which the gills are blue at first. If you have a dry, radially fibrillose indigo cap with a distinct pointed peak, blue gills flushing salmon, a fibrillose blue stipe with no ring, and a pink print, Entoloma hochstetteri is the reading that fits every character at once.