Clustered Bonnet

The Clustered Bonnet is one of the larger and more strongly clustered species of Mycena, a huge genus of small, fragile, conical- to bell-capped mushrooms in the family Mycenaceae. Most bonnets grow singly or in scattered troops; this one packs into tight tufts of a dozen or more fruitbodies from a single point on dead hardwood.

It is a fungus of old oak and sweet chestnut, appearing year after year on the same stumps and fallen trunks, often forming impressive colonies that ring the cut surface or emerge from bark crevices. Fruiting continues late in the year, so it is one of the bonnets still to be found after the main autumn flush is over.

Two characters make it stand out from its many relatives: the cap margin, which is scalloped and finely toothed rather than smooth, and the stem, which passes from white at the top through bright yellow-ochre to a rich rusty or reddish brown at the base.

Cap

1–4.5 cm across, at first conical to bell-shaped with the margin pressed to the stem, expanding to broadly bell-shaped or campanulate with a low umbo. Pale grey-brown, buff or greyish, usually darker at the centre and paler toward the edge, and marked with translucent radial lines when moist. The margin is distinctly scalloped and bears small, sharp, whitish teeth on young caps — the best single field character.

Gills

Adnate with a short decurrent tooth, moderately spaced, fairly broad, whitish becoming pale grey or with a faint pinkish flush, and with paler, even edges. Short intermediate gills are present.

Stipe

3–10 cm long and only 1.5–4 mm thick, hollow, smooth, straight or slightly curved. White to pale grey at the apex, quickly becoming golden yellow to yellow-brown in the middle, and rusty orange to deep reddish brown toward the base, which is clothed in coarse white woolly hairs binding the tuft together.

Flesh and spore print

Flesh is thin, pale and watery, with a mealy to slightly rancid smell in mass. There is no milky exudate and no dramatic bruising reaction. The spore print is white.

Almost always on dead hardwood, with a marked preference for oak and sweet chestnut; beech and other broadleaf trees are occasional hosts. It grows on stumps, cut surfaces, exposed roots and fallen trunks, favouring wood that is already well rotted but still firm, and it can also emerge from the base of standing dead trees.

Fruitbodies come in dense tufts of five to fifty, often several tufts on one stump. The species is common through temperate Europe and is recorded across Asia and North America. The main season runs from late summer through autumn and often into early winter, with fruitings triggered by rain after mild spells.

Mycena inclinata is a saprotroph, decomposing the lignin-rich wood of old hardwood stumps and contributing to a slow white rot that leaves the timber pale and fibrous. It works on wood in the middle to late stages of decay, following the larger bracket fungi that opened up the trunk.

The tufted habit reflects the way the mycelium fruits from a concentrated point where it has colonised a rich pocket of wood, and the woolly stem bases fuse into a common felted mat. Wind-dispersed white spores establish new colonies on freshly exposed dead hardwood, and a well-colonised stump may fruit annually for several years.

The Common Bonnet (Mycena galericulata) is the closest match and also grows in tufts on hardwood, but it is tougher, has a smooth (not toothed) cap margin, gills that flush distinctly pink with age, and a stem that stays grey-brown to blackish without the golden and rusty zones. Mycena maculata develops reddish-brown spots on cap and gills and lacks the toothed margin.

Mycena polygramma has a striking silvery, longitudinally grooved stem and grows more sparsely. Young Honey Fungus (Armillaria) clusters share the habitat but are far more fleshy, have a ring on the stem and scaly cap centres. Small Psathyrella species on stumps are separated by their fragile, dark brown to blackish spore print and quickly darkening gills.