Blue Band Brittlegill

The Blue Band Brittlegill, Russula azurea, is one of the softer-coloured members of a genus better known for scarlets and purples. Its cap carries washes of lilac, slate-blue and azure over a pale ground, frequently with an ochre or cream centre, and the whole surface is covered by a fine pruinose bloom that gives it a frosted, slightly powdery look.

It is a conifer species, most often found with spruce on damp acid soils, and this habitat preference is one of the most useful separators from the superficially similar grey-blue brittlegills of broadleaf woodland. Its fruit bodies tend to be modest in size and rather fragile compared with the heavier brittlegills of oak woods.

Like all Russulaceae it has granular flesh made of rounded cells, so the stipe snaps cleanly and the gills shatter rather than tear. Colour in the group is notoriously plastic, so identification relies on habitat, cap texture and the pale spore deposit together rather than on any single feature.

Cap

Usually 3-7 cm across, convex then flattening and often shallowly depressed at the centre. The surface is dry and matt, covered by a fine whitish bloom that can be rubbed away. Colour is lilac, violet-blue, slate or azure, commonly mixed, and very often fading to ochre, cream or pale buff over the disc. The cuticle peels partway from the margin, which stays smooth for a long time and only becomes faintly grooved when old.

Gills

White, staying white or barely creaming, moderately crowded, narrow and adnexed. They are brittle in the usual manner and may fork occasionally near the stipe. Gill edges are entire.

Stipe

3-6 cm long and around 1-1.5 cm thick, white, smooth and often finely pruinose like the cap, sometimes with a faint bluish or greyish flush towards the apex. It is cylindrical or slightly narrowed downwards, soon becoming stuffed and rather fragile, without ring or volva.

Flesh & spore print

The flesh is white, moderately thin and unchanging when cut, perhaps greying very slightly in age. The spore print is white to the palest cream, paler than that of most grey-capped broadleaf brittlegills. Spores are ellipsoid with warts joined into a partial network.

Russula azurea is mycorrhizal with conifers, particularly spruce, and to a lesser extent fir and pine. It grows on damp, acid, humus-rich soils in mature plantation and natural conifer forest, often among mosses and needle litter, and is commonest in upland and northern regions where spruce forest dominates.

Fruiting runs from late summer into autumn, with the main flush from August to October. The species is distributed through northern and central Europe and into montane forest further south, following the natural and planted range of spruce.

This species forms ectomycorrhizal partnerships with conifer roots, wrapping the fine root tips in a fungal mantle and growing between the outer cells of the root cortex. Through this interface the fungus supplies mineral nutrients and water while receiving sugars from the tree, an exchange that is especially valuable in cold, acid, slow-decomposing forest soils where nutrients are locked up in organic matter.

Spruce forests support large communities of brittlegills, milkcaps and webcaps, and together their mycelia form an extensive underground network that stabilises soil and moves nutrients between trees and litter. The relatively soft fruit bodies of this species are rapidly grazed by slugs and colonised by fungus gnat larvae before breaking down into the moss layer.

The Powdery Brittlegill (Russula parazurea) is the closest match in appearance but is a broadleaf species of oak and lime, has a greyer, more olive-green cap and produces a distinctly cream spore print. The Charcoal Burner (Russula cyanoxantha) is much larger, with a greasy mottled cap and soft flexible gills that bend rather than break.

Russula caerulea, the Humpback Brittlegill, is another conifer species with a dark purple cap but is easily separated by its pronounced central umbo and its ochre spore deposit. Russula ionochlora is a small broadleaf species with a lilac-and-green cap and a cream print. Cap bloom, host tree and the near-white spore deposit together identify the Blue Band Brittlegill.