Charcoal Burner Identification Guide

The First Impression

You are in a mature beech or oak wood in late summer, on leaf litter rather than wood, and there is a stout mushroom with a broad cap in a colour you would struggle to name — part slate-violet, part olive-green, part wine-purple, sometimes with grey and lilac washed together over the same cap like a pigeon's neck. The stem is chalk white and thick, the mushroom sits firm and squat, and when you pick it there is no ring, no volva and no woolly veil. That combination of a brittle white stem, a variable duskily coloured cap and a woodland-floor habitat puts you in Russula immediately. Getting from Russula to Russula cyanoxantha is a matter of a single gill test, backed up by a spore print.

Reading the Cap

Size and shape. Typically 5 to 15 cm across, occasionally larger. Convex and slightly domed at first, then flattening, and finally shallowly depressed in the centre in mature specimens, with the margin staying fairly even and only faintly grooved in age.

Colour. This is the least reliable character, and knowing that is part of the identification. The classic form mixes violet, lilac, slate-grey, olive and green in irregular radial streaks, often darkest in the centre. There are forms that are almost entirely green, others that are wine-purple or nearly blackish-violet, and old sun-faded caps can bleach to dull ochre-grey. Do not try to identify this species on colour.

Surface. Slightly greasy or tacky when wet, drying matte. The cuticle is often finely radially veined, streaked or slightly pitted, particularly towards the margin, which gives the cap a faintly grained look under a hand lens.

Cuticle peeling. Lift the skin at the margin with a thumbnail. In this species it strips back roughly a third to halfway to the centre, revealing flesh that may be faintly lilac-tinted just under the skin.

The Gills — The Decisive Test

Every Russula has brittle flesh, and in nearly all of them the gills are brittle too: run a finger across them and they shatter into fragments. Russula cyanoxantha is the great exception, and this is the character the whole identification rests on.

Draw a thumb sideways across the gills. They feel greasy or slightly lardy, and instead of crumbling they bend, splay and spring back. They are pliable. If the gills shatter, the mushroom is not cyanoxantha, no matter how convincing the cap colour.

The other gill features: white to cream, never yellow or ochre; fairly crowded; adnexed to almost free; and conspicuously forked, especially near the stem attachment, with some forking further out too. Old gills may pick up dingy grey-brown bruises where handled, but they do not develop rusty spotting.

The Stipe, Base and Flesh

The stem is 4 to 10 cm long and 1.5 to 3 cm thick, cylindrical or slightly clavate, white, and often flushed with a faint lilac or purplish tint towards the base in richly coloured specimens. It is firm and solid when young, becoming softly stuffed and finally chambered. Snap it in half rather than cutting: it breaks cleanly and crisply, like a stick of chalk, with no fibrous stringing. There is no ring and no basal bulb or sac; the base tapers or is bluntly rounded and is usually flushed with grey where soil has been in contact.

The flesh is white and firm. Watch a cut surface for several minutes: it stays white or greys very slowly and slightly, particularly in the stem base of older specimens. There is no latex — no milk of any colour seeps from a cut, which separates the whole genus from Lactarius. The odour is mild and unremarkable.

If you carry chemicals, a drop of iron salt solution on the stem flesh is useful: in this species the reaction is negligible or turns faintly greenish, whereas most similar Russula species go a clear salmon-pink. It is a two-second test that resolves a lot of arguments.

Taking a Spore Print

Cut the stem off flush with the gills, set the cap gills-down on paper that is half white and half black, cover with a cup and leave it for four to eight hours. Russula identification depends heavily on the exact shade of the print, so a thick deposit on a dark background matters more here than in most genera.

Russula cyanoxantha gives a pure white print, at most with the barest cream tint — the palest end of the Russula range. Anything with a definite cream, ochre or yellow cast points somewhere else in the genus. Under the microscope the spores are broadly ellipsoid, around 7 to 9 by 5 to 7 micrometres, ornamented with low warts and fine connecting lines that stain blue-black in iodine reagents.

Substrate and Season

This is an ectomycorrhizal partner of broadleaved trees, above all beech, with oak, hornbeam and birch also common. It fruits on soil and leaf litter, never on wood, singly or in loose scattered groups, from early summer through to late autumn, peaking after summer rain. It is one of the most abundant large Russula species in mature deciduous woodland across Europe and occurs in comparable habitat elsewhere in the north temperate zone.

Separating It From Look-Alikes on Morphology Alone

Russula grisea and Russula ionochlora. Both share the grey-violet-green cap palette. Both have brittle gills that shatter under a thumb, and both drop a cream-tinted print rather than pure white. The flexible-gill test separates them.

Russula parazurea. Cap a dull blue-grey to greenish, distinctly pruinose or bloomed, as if dusted with fine powder. Gills brittle, print cream. The powdery cap surface and the crumbling gills are enough.

Russula virescens. Green cap that breaks up into distinct angular patches or crazed plates, giving a mosaic surface unlike the smooth or radially veined cap of cyanoxantha. Gills brittle, print white to pale cream.

Russula variata. In North America this is the closest analogue: similarly variegated purple-green caps and heavily forked gills. Its gills, however, are more consistently and repeatedly forked throughout, not just near the stem, and they are less pliable.

Russula atropurpurea and other dark purple species. Uniformly deep purple-black centred caps, brittle gills, and often a stem greying strongly with age.

Other genera. Lactarius species bleed latex from cut gills. Brittle-fleshed Russula never does. Anything with a ring, a volva, free gills and a dark print belongs elsewhere entirely.

A Field Sequence That Works

1. Confirm the genus: brittle chalk-snap stem, no ring, no volva, no latex, on soil.
2. Ignore the cap colour; note the greasy surface and half-peeling cuticle.
3. Run a thumb across the gills. They must flex, not shatter.
4. Check for forking near the stem attachment.
5. Take a print on dark paper and confirm pure white.
6. Confirm a beech or oak partner nearby.