Clustered Bonnet Identification Guide

The First Encounter

Clustered Bonnet is a late-autumn fungus of dead oak, and the scene is usually a mossy stump, a fallen trunk or a cut log in mixed woodland, often in the same place year after year. What you see first is a dense mound of small pale mushrooms erupting from a single crack or cut face, twenty or fifty fruit bodies packed shoulder to shoulder, their stipes all leaning outward from a common point so the tuft flares like a bunch of flowers stuffed into a narrow vase. The caps are small, conical to bell-shaped, and pale enough to catch the eye against dark wet bark.

That combination - a tight caespitose tuft, small bell-shaped caps and long slender stipes - places the find in the bonnets, the genus Mycena, and specifically among the handful of Mycena that grow in crowded tufts on wood. Most bonnets are scattered singletons on litter or moss; clustered wood-dwellers are a small subset, and separating them is a matter of three or four careful checks.

Reading the Cap

Caps are 1-4 cm across, conical or ovoid at first and expanding to bell-shaped, usually retaining a distinct blunt umbo. The surface is finely radially grooved or striate from the margin towards the centre, so that the gill positions show through as translucent lines in wet weather. Colour is variable: whitish, grey-buff or pale cream at the margin, warming to grey-brown, ochre-brown or reddish-brown at the centre, and specimens dry to a paler and duller version of themselves.

Now take a hand lens to the edge of a young, expanding cap. In this species the cap margin carries small, blunt, tooth-like projections, so it looks finely scalloped or crenulate rather than cleanly cut. This denticulate margin is the best single cap character, and it is easiest to see on caps that have just begun to open, before weathering wears the teeth away. Combined with the growth habit, it does most of the identification work.

Reading the Gills

The gills are moderately spaced, fairly broad, and attached adnately, usually with a small decurrent tooth running a very short way onto the stipe. When young they are whitish to pale grey; with maturity they take on a pinkish or flesh-toned cast, and the edges are typically paler than the faces. Look along the gill faces with a lens for cross-veining: in this species interveining is slight or absent, whereas some relatives develop conspicuous cross-veins between the gills as they age.

The gill tissue is delicate. These are fragile, thin-fleshed mushrooms and the caps break easily, so handle specimens by the stipe.

Reading the Stipe and Base

The stipe is long relative to the cap - 4-10 cm and sometimes more - slender, 2-4 mm thick, cylindrical, smooth and polished, and hollow throughout. It is also tough and springy, resisting a straight pull far better than the cap suggests, a general trait shared across the tough-stemmed small woodland fungi.

The colour gradient along the stipe is the second key character. The apex is white to very pale cream. Below the middle it warms through yellow-ochre to a rich golden brown, and the lower quarter darkens to reddish-brown, rust, or almost mahogany in older specimens. The whole gradient can be read at a glance on a tuft where fruit bodies of different ages sit together, and it is far more pronounced than in most bonnet species.

Finally, look at the very base with a lens. The bases of the fused stipes are covered with coarse, stiff, whitish hairs - a strigose base - which mat together and bind wood fragments and moss where the tuft emerges. Feel it: it is rough rather than smooth or bald.

Flesh, Colour Change and Odour

Cut a stipe across. The flesh is thin, whitish to pale brownish, and hollow-centred. Nothing bleeds. There is no latex, no milk, no coloured juice, and this absence is important because it is the fastest way to eliminate one of the closest look-alikes. Cut surfaces do not change colour in any dramatic way.

Crush a handful of caps and stipes and smell them immediately. The odour is distinctive but hard to name: generally described as rancid or mealy, and often reported as reminiscent of candle wax or tallow with a faint iodine note, especially as the material begins to dry. A tuft of freshly gathered specimens left in a paper bag for ten minutes usually makes the smell obvious.

Taking a Spore Print

These caps are small and thin and drop relatively few spores, so pool several. Snip five or six caps free and lay them gills down together on a single sheet of black card under a cover for six hours or overnight; pooling gives a readable deposit where one cap alone would give almost nothing. The print is white. Confirm by tilting the card against the light. A brown, rust or purple-brown deposit rules the species out entirely and points instead to the brittlestems and their relatives, which is by far the commonest error with small tufted stump fungi.

Substrate, Season and Habitat

Clustered Bonnet is a saprotroph of dead broadleaf wood with a strong preference for oak, and it is also frequent on sweet chestnut. Look on stumps, cut ends of felled logs, buried roots and fallen trunks in mixed and deciduous woodland, especially where the wood is well rotted but still solid enough to hold its shape. It sometimes appears to grow from bare soil when the substrate is a buried root, so scrape gently at the base if the wood is not obvious.

The season is late. It runs from late summer into late autumn and often continues into early winter, persisting well past the first frosts and frequently being one of the last fungi still fruiting in the wood in December in mild years.

Separating It from Look-alikes

Common Bonnet, Mycena galericulata. The closest and most frequent confusion. It grows on the same oak stumps in the same season, but usually in smaller, looser groups of two to six rather than dense many-stemmed tufts. Its cap margin is even and lacks the tooth-like projections. Its stipe is more uniformly grey-brown without the strong pale-to-rust gradient. And its gills develop conspicuous cross-veins between them with age, a character that is weak or absent in Clustered Bonnet.

Burgundydrop Bonnet, Mycena haematopus. Also tufted on dead hardwood, also with a denticulate cap margin, and superficially very close. The separation is instant: break a stipe and a dark reddish-brown juice beads out of the break. Clustered Bonnet never bleeds. Burgundydrop Bonnet is also more uniformly wine-brown across cap and stipe.

Grooved Bonnet, Mycena polygramma. Solitary or in very small groups rather than tufted, with a stipe that is silvery-grey and conspicuously longitudinally grooved and striate - run a nail up it and you feel the ridges. Its cap is greyer and its base is rooting rather than hairy-tufted.

Common Stump Brittlestem, Psathyrella piluliformis. Forms very similar dense tufts on hardwood stumps at the same season, but the caps are date-brown and strongly hygrophanous, fading dramatically to buff from the centre outwards, the flesh is extremely brittle rather than tough, the gills darken to purplish-brown, and the spore print is dark purple-brown. The print alone separates them beyond doubt.

Honey fungus, Armillaria species. Also tufted on stumps in autumn, but far larger and fleshier, with a ring on the stipe and a scaly cap centre.