Fragile Brittlegill

Russula fragilis, the Fragile Brittlegill, lives up to its name: the thin-fleshed cap shatters at a touch and the slender stipe crumbles when picked. It is one of the commonest small brittlegills of damp temperate woodland and one of the most variable in colour, which makes its single microscopic-scale field character particularly valuable.

That character is the gill edge. Viewed with a hand lens against the light, the edges of the gills are finely toothed or serrated rather than smooth — a feature shared by very few other brittlegills and one that can be checked in the field with a x10 lens.

The species sits in the Russula emetica group of fragile, white-spored, easily peeling brittlegills. Its colour range runs from deep violet-purple and wine-red through blackish, olive-green and grey to almost pure white, sometimes with several tones on a single cap.

Cap

Small, generally 2-5 cm across, convex then flat and often depressed at the centre. The surface is smooth and greasy when moist. Colour is exceptionally variable: violet-purple, wine, blackish-purple, olive-green, grey-brown, straw or nearly white, very often with a darker or contrastingly olive centre. The cuticle peels easily almost to the middle, and the thin margin becomes clearly grooved with age.

Gills

White, staying white or barely creaming, fairly crowded to moderately spaced, adnexed, and very brittle. The diagnostic feature is the edge: under a hand lens the gill margins are minutely serrated, like the edge of a fine saw. This is best seen on a fresh specimen by holding a gill up to the light.

Stipe

Slender and very fragile, 3-6 cm long and 0.6-1.5 cm thick, white, smooth, often slightly swollen towards the base, soon becoming hollow. It may grey slightly with age. There is no ring or volva.

Flesh & spore print

Thin, white, brittle flesh that does not change colour when cut. The spore print is white to the palest cream. Spores are broadly ellipsoid with tall warts linked by fine lines into a partial network.

The Fragile Brittlegill is mycorrhizal with a broad range of trees — birch, oak, beech and various conifers including spruce and pine. It favours damp, acid to neutral ground and is often found in moss, among leaf litter in shaded hollows, on the banks of woodland ditches and in mixed plantations.

Fruiting is prolonged, from July through to November, and this is one of the brittlegills most likely to be found late in the season. It is very common throughout Europe and widespread across temperate and boreal regions of the northern hemisphere.

This species forms ectomycorrhizas with the fine roots of its host trees, sheathing the root tip in a fungal mantle and growing between the outer root cells. Nutrients and water gathered by the extensive hyphal network are traded for sugars from the host, a partnership that benefits both organisms and is particularly important on the poor acid soils this species favours.

Its wide host range and tolerance of damp shaded ground make it one of the most consistently present mycorrhizal fungi in mixed woodland. The delicate fruit bodies last only a few days, collapsing quickly and returning their nutrients to the litter, where they are worked over by springtails, mites and fly larvae.

The Purple Brittlegill (Russula atropurpurea) has a similar blackish-purple cap but is larger and firmer, with a cream spore print and entire, unserrated gill edges. The Birch Brittlegill (Russula betularum) is comparably fragile but has a much paler rose-pink cap, smooth gill edges and grows only with birch.

Russula gracillima is another slender birch species, with a cap mixing pink and olive-grey and a paler, sometimes pink-tinged stipe. The Sickener (Russula emetica) is larger and a purer scarlet, with more distant gills and smooth edges. Checking the gill edges with a hand lens is the quickest way to confirm R. fragilis against all of these.