Entoloma hochstetteri

Entoloma hochstetteri is one of the most instantly recognisable fungi in the world, thanks to a cap coloured an intense indigo to turquoise blue that looks almost artificial against the brown of the forest floor. In New Zealand it carries the Maori name werewere-kokako, a reference to the blue wattle of the kokako bird, and the species has appeared on postage stamps and banknotes as an emblem of native forest.

Despite its exotic appearance the fungus is a fairly typical member of the genus Entoloma, a very large group in the family Entolomataceae characterised by pink spore deposits and angular spores that are many-sided when viewed under a microscope. Most entolomas are drab grey, brown or straw-coloured; a handful, including this species and a few relatives in Asia and the Americas, have evolved striking blue pigments in the cap cuticle.

What makes the species distinctive in the field is the combination of blue colour and pink gills. As the fruit body matures the pink spores dust the gill faces, so a fresh specimen shows a blue cap and stipe over gills that shift from bluish-grey to salmon-pink, a colour contrast that no other common forest mushroom reproduces.

Cap

The cap is 2-6 cm across, at first sharply conical or bell-shaped, later expanding to broadly convex with a persistent pointed umbo. The surface is dry, finely fibrillose to slightly scaly at the centre, and coloured deep indigo, sapphire or greenish-blue; the fibrils often run radially, giving a streaked look. Older or rain-washed caps fade towards dull blue-grey or olive at the disc while the margin stays blue.

Gills

Gills are adnexed to almost free, moderately spaced and rather broad. They begin bluish or greyish-blue with a paler edge and turn progressively pink, then salmon or dull flesh-pink, as the spores ripen. This pink maturity is one of the most reliable characters for placing the species in Entoloma.

Stipe

The stipe is 3-7 cm long and only 3-8 mm thick, cylindrical, hollow with age, and coloured the same blue as the cap or a little paler. It is longitudinally fibrous, often with fine bluish fibrils lying along its length, and the base carries a small tuft of white to pale blue mycelial down. There is no ring and no volva.

Flesh and spore print

The flesh is thin, fragile and pale blue in the cap, whitish towards the stipe base. It does not change colour appreciably when cut and does not exude latex. The spore print is pink; the spores themselves are angular and many-sided, a defining microscopic feature of the family.

This fungus grows on the ground among leaf litter, moss and rotting debris in damp native forest, favouring shaded gullies, stream banks and mossy roadside cuttings where humidity stays high. It is strongly associated with broadleaf-podocarp and southern beech forest in New Zealand, and closely similar blue entolomas are recorded from parts of India and the wider Indo-Pacific region.

Fruiting is typically solitary or in small scattered groups rather than large troops, and peaks in the cooler damp months from autumn into winter. Because the fruit bodies are small and slender they are easily overlooked despite the vivid colour, and they collapse quickly after heavy rain or frost.

Entoloma hochstetteri is generally regarded as mycorrhizal, forming nutrient-exchange partnerships with the roots of native forest trees, though some members of the genus are litter decomposers and the exact strategy of this species is still debated. Its consistent occurrence under established native canopy rather than in disturbed or exotic plantings supports a partnership with long-lived forest trees.

The life cycle follows the standard agaric pattern: pink angular spores released from the gills germinate in the litter layer, hyphae fuse to form a mycelium, and under suitable moisture and temperature the mycelium produces the short-lived blue fruit bodies. The blue pigments are azulene-type compounds that appear to be produced in the cap cuticle and stipe surface rather than throughout the flesh.

Few fungi share the vivid blue cap, but several can cause confusion. Blue-capped species of Mycena, such as the small Mycena species with bluish stipes, are much more slender and fragile, grow on wood or twigs rather than soil, and keep white gills and a white spore print throughout life. Small Cortinarius species with blue-violet colours, common in the same forests, differ in having a cobwebby cortina over the young gills and a rusty-brown spore deposit that stains the upper stipe.

Other Entoloma species in the same habitat share the pink spore print and angular spores but are grey, brown or white rather than blue. Faded, rain-leached specimens of E. hochstetteri that have lost most of their colour are best confirmed by the pink gills, fibrous hollow stipe, absence of a ring or volva, and pink spore print taken on white paper.