Greencracked Brittlegill Identification Guide

The Setting and the First Glance

You are most likely standing in warm broadleaf woodland in mid to late summer, under oak, beech, chestnut or hornbeam, on a path edge or a slightly open slope with thin litter. What catches the eye is a firm, dome-shaped cap the colour of old verdigris, with the surface broken into small angular patches on a paler ground, as though the skin were crazed glaze on a pot or dried mud on a riverbank. It sits solidly in the litter, single or in twos and threes, and it does not have the flimsy look of most green fungi. That combination of firmness plus a mosaic-cracked green cap is the whole species in one impression, and everything that follows is confirmation.

The Cap, Patch by Patch

The cap is 5 to 12 cm across and occasionally larger, hemispherical at first, then convex and finally flattened with a shallow central depression. It is hard and heavy for its size. The skin is dry and matt, never greasy or slimy, and its defining feature is areolate cracking: the surface separates into small angular to rounded patches, densest at the centre and becoming sparser or fading out near the rim, with the paler cream flesh showing in the gaps. Patch colour runs from grey-green through verdigris to bluish or olive green, sometimes with faint ochre in the mix, and it is usually strongest at the centre. The margin stays smooth and even, without pronounced grooves, though very old caps may show faint striation. The skin peels only a short way in from the edge, which is worth testing.

Gills, Attachment and the Brittleness Test

Underneath, the gills are white to pale cream, moderately crowded, adnexed to almost free at the stipe, fairly narrow, and often forked near the stipe with occasional cross-veining between them at the base. Edges are even. The essential test is mechanical: draw a fingertip sideways across the gill faces. In a brittlegill the gills shatter into short fragments rather than bending, because the flesh is built of rounded cells rather than long fibres. Doing this deliberately on every green mushroom you meet is the fastest way to separate brittlegills from everything else in the wood. Damaged gills may slowly discolour to pale brown but do not turn grey, black or red.

Stipe, Base and Flesh

The stipe is 4 to 9 cm long by 1.5 to 3 cm thick, cylindrical or slightly club-shaped, and pure white when young, ageing to buff and often browning a little near the base. Its surface is dry and finely wrinkled or minutely powdery to the touch, and there is no ring, no ring zone and no bag or volva at the base. Dig the whole fruit body out to confirm that the base is simply rounded and set into soil. Snap the stipe in half rather than twisting it: it breaks cleanly, like a piece of chalk, another expression of the same cellular structure. The flesh is white and firm throughout, becoming softer and slightly cavernous in the stipe of old specimens, and it does not change colour appreciably on cutting. At most, cut surfaces go dull cream or slowly acquire a brownish tone at the stipe base. There is no latex, and the odour is faint and pleasantly fungal.

Taking and Reading the Spore Print

Spore print colour is a working character in this group, so take the print properly. Cut the cap from the stipe, lay it gills down on white paper, cover it with a bowl or upturned glass, and leave it for four to eight hours or overnight in a cool place. Scrape the deposit into a compact heap with a blade before judging the colour, because a thin scatter always looks paler than it is, and read it in daylight against white paper. For this species expect white to pale cream. Under the microscope the spores are broadly ellipsoid, roughly 6 to 9 by 5 to 7 micrometres, ornamented with warts up to about half a micrometre high joined by fine connecting lines that form an incomplete network, and the ornamentation blackens in iodine solution.

Substrate, Partners and Season

The fungus forms mycorrhizal partnerships with broadleaf trees, so it fruits from soil and never from wood. Record the trees present: oak, beech, sweet chestnut, hornbeam and lime are the usual associates, on well drained, often slightly acid to neutral soils in warm situations. Old parkland, wood pasture, sunny woodland edges and open rides are more productive than dense shaded interiors. The season is early, typically running from midsummer through to early autumn, and a warm wet spell in July or August will often produce fruit bodies weeks before the main autumn flush of other species. Fruit bodies are frequently solitary or in small scattered groups rather than large troops.

Separating It From Look-alikes on Morphology Alone

The green brittlegills are the main comparison set, and they are separated on cap surface, gill behaviour and spore print tone.

Russula aeruginea has a smooth, slightly greasy, uniformly grass-green to olive cap with no patchwork cracking, is generally more slender, associates strongly with birch, often shows rusty spotting on the gills, and gives a cream spore print. Russula crustosa does crack, but its patches are ochre, tan and olive rather than clean verdigris, the cracking is finer and covers the cap more evenly, and its print is cream. Russula heterophylla is green to grey-green with a smooth, faintly greasy, uncracked cap, narrow crowded forking gills, a white print, and a stipe base that browns readily. The green form of Russula cyanoxantha is the classic trap: the cap may look similar in colour but is smooth rather than mosaic-cracked, and above all its gills are soft, flexible and slightly greasy to the touch, bending under a finger instead of shattering.

Outside the brittlegills, the fungus most often confused on colour alone is Amanita phalloides, and the architecture is entirely different. It has free white gills that never take on a cream tinge, a fibrous stipe that tears in strands rather than snapping like chalk, a skirt-like membranous ring hanging from the upper stipe, and a conspicuous sac-like volva enclosing the swollen base, which only shows if the fruit body is dug out rather than pulled. Its cap is smooth, silky and radially streaked, not broken into patches. Digging every green mushroom out to the base and testing the gills between finger and thumb resolves this pair immediately.

A Working Sequence

Check for a dry, mosaic-cracked green cap; confirm gills and stipe shatter rather than bend or tear; dig to confirm a plain rounded base with no ring and no volva; note the broadleaf partners; then take an overnight print and read it as white to pale cream. Five steps, in that order, and the record is secure.