Bluing Bolete

The Bluing Bolete produces one of the most dramatic colour reactions in the whole fungal kingdom: a pale, almost bleached-looking mushroom that turns deep cornflower to indigo blue wherever it is handled, so quickly that the change can be watched in real time. Fresh specimens carried in a basket arrive covered in blue fingerprints.

It belongs to Gyroporus, a small pale-spored genus in the family Gyroporaceae, distinguished from the mainstream boletes by brittle flesh, a chambered and eventually hollow stipe, and a straw-yellow rather than olive-brown spore print. Within the genus it is separated from its chestnut-coloured relatives by its pallor and its shaggy cap surface.

It is a fungus of poor, sandy, acid ground, and its presence usually signals heath, dune-slack woodland or sandy birch and pine country rather than rich woodland loam.

Cap

Convex then flattening and often irregular or lobed, 4–12 cm across. The surface is dry and distinctly coarse: fibrillose, scurfy or almost woolly, sometimes with small raised tufts, and frequently uneven or pitted. Colour is pale straw, buff, dirty cream or pale ochre-yellow, sometimes darkening to dull tan with age. The slightest touch produces a deep blue mark.

Pores

Small and round, white to pale straw yellow, turning instantly and intensely cornflower to indigo blue where bruised. The tube layer is short and pale, and it too blues immediately in section.

Stipe

Roughly equal or swollen in the lower half, 4–10 cm tall, concolorous with the cap and similarly fibrillose or scurfy. Internally it is at first stuffed with cottony tissue, then divided into irregular chambers, and finally hollow. It snaps brittlely like a piece of chalk rather than tearing.

Flesh and spore print

White and brittle, changing within a second or two of cutting to a vivid deep blue that suffuses the whole section and then slowly fades to grey-blue over many minutes. The spore print is pale straw to lemon yellow.

Gyroporus cyanescens grows on poor, sandy or gravelly acid soils, associating with birch, oak, beech and pines. Typical sites include sandy heaths and commons, birch scrub on old sand and gravel workings, dune woodland, and the edges of pine plantations on light ground; it frequently appears on bare eroded banks and along sandy tracks.

Fruiting runs from midsummer through to late autumn. It is widespread but rather local across Europe and northern Asia, and occurs across eastern North America, where similar pale bluing Gyroporus taxa have also been segregated.

This is an ectomycorrhizal fungus whose mycelium forms sheaths on the fine roots of birch, oak and pine and ramifies through nutrient-poor sand. On such substrates, where organic matter is thin and nutrients leach rapidly, the mycorrhizal network is a major route by which trees obtain phosphorus and nitrogen, and it also stabilises loose sand by binding grains together with hyphae.

The striking blue pigmentation is produced by rapid oxidation of colourless precursors in the flesh when they are exposed to air, a chemistry shared in weaker form by many boletes but expressed here with unusual speed and intensity. Fruit bodies persist only a week or so before collapsing, and the brittle hollow stipe breaks down quickly into the litter.

The Chestnut Bolete (Gyroporus castaneus) shares the brittle, hollow stipe and pale straw spore print but has a rich chestnut-brown, smoothly suede-textured cap and flesh that does not change colour at all. Gyroporus purpurinus is smaller with a wine-red to purple cap.

Among the true boletes, blue-staining species such as Neoboletus luridiformis have solid fibrous stipes, red or orange pores and olive-brown spore prints. Leccinum species growing in the same sandy birch woods have whitish pores and stipes roughened with dark scabers, and Xerocomellus species are smaller with cracked caps and olive-brown prints.