Sky Blue Mushroom

The Sky Blue Mushroom is one of the emblematic fungi of New Zealand and among the most saturated blues in the whole fungal kingdom. A mature specimen looks almost artificial: a slender conical cap of deep indigo to sky blue, streaked with darker radiating fibres, on a matching blue stalk rising out of dark forest litter.

It belongs to Entoloma, an enormous genus in the family Entolomataceae defined by pink spore deposits and, under the microscope, spores that are angular in outline rather than round or elliptical. In this species the pink of the maturing spores gradually overlays the blue of the young gills, producing an odd lilac to salmon transition that is itself a good identification cue.

The blue colour is produced by azulene-type pigments in the tissue. The species is well enough known in New Zealand to appear on the country's fifty-dollar note and carries the Maori name werewere-kokako, referencing the blue wattle of the kokako bird.

Cap

Small, generally 1-4 cm across, conical to bell-shaped when young, expanding to broadly conical or flat with a low pointed umbo. The colour is deep indigo, Prussian blue or brilliant sky blue, generally darkest at the centre, and the surface is dry and radially fibrillose, with fine darker fibres running from centre to margin. Older or weathered caps fade toward greenish blue, dull grey-blue or brownish, particularly in dry weather.

Gills

Adnexed to narrowly attached and fairly well spaced, blue to blue-grey when young and becoming distinctly pink, salmon or lilac-flushed as spores ripen. The gill edges often keep a bluer tone than the faces, and the contrast between blue edge and pinkish face on a mature specimen is characteristic.

Stipe

2-6 cm long and slender, sometimes slightly compressed or grooved, coloured the same blue as the cap or a shade paler, dry and finely fibrous. It is hollow, lacks any ring or volva, and the base usually carries a small tuft of white to bluish basal mycelium binding leaf litter.

Flesh & spore print

Flesh is thin, pale bluish and unchanging when cut. The spore print is pink; under a microscope the spores are conspicuously angular with several flat facets, the standard microscopic signature of the genus.

Entoloma hochstetteri is a litter-dwelling species of damp, shaded native forest. In New Zealand it grows on the forest floor among moss, fallen leaves and rotting twigs in beech (Nothofagus) forest and in mixed podocarp-broadleaf forest with rimu, tawa and kamahi, favouring humid gullies, stream banks and track-side banks where the litter stays wet.

Fruitbodies appear singly or in small scattered groups, typically from autumn into winter and after periods of heavy rain, though records span a wider window in consistently wet forest. The species is best documented from both main islands of New Zealand, with closely related or possibly conspecific blue entolomas reported from Australia and parts of Asia, including India.

The species is generally regarded as a litter saprotroph, breaking down leaf and twig debris on the forest floor, with the white basal mycelium visibly binding litter fragments at the stipe base. Some members of Entoloma form associations with plant roots and a mycorrhizal or partly biotrophic lifestyle has been suggested for this one as well, so its precise nutritional strategy is not fully settled.

Whatever its exact mode, it is confined to intact, humid, undisturbed native forest and does not colonise pasture, exotic plantations or garden mulch, which makes it a useful indicator of well-preserved forest floor habitat. Spores are released from the gills in the usual way for an agaric and dispersed by air movement close to the ground; the striking blue pigment appears to serve no dispersal function and is likely a by-product of tissue chemistry.

Mycena interrupta, the pixie's parasol, is the blue mushroom most often confused with it: it is much smaller, has a hemispherical, translucent-striate, sticky sky-blue cap, grows in tight clusters directly on rotting wood, and gives a white spore print with white gills that never flush pink. Other blue Entoloma species in the region, such as Entoloma virescens, are separated by cap shape, degree of umbo and gill spacing, but share the pink print.

Cortinarius rotundisporus and its relatives can look blue-green in youth but develop a rusty-brown spore deposit, cobwebby veil remnants on the stipe and a slimy cap. Waxcaps in Gliophorus may be blue-green but have thick, waxy, widely spaced decurrent gills, a viscid slimy surface and a white spore print. Checking gill attachment, spore colour and whether the fungus arises from litter or from wood resolves all of these.