Common Bonnet

The Common Bonnet is one of the largest, toughest and most persistently encountered members of Mycena, and for many people it is the species that introduces the genus. It appears on hardwood stumps from spring right through to the first hard frosts, and its cartilaginous stipe and grooved bell-shaped cap are a familiar sight on almost any decaying deciduous stump.

Unlike the many ephemeral bonnets that collapse within a day, M. galericulata is comparatively substantial and long-lasting, with a stipe that resists snapping and a cap that holds its shape well. The specific epithet refers to a small cap or helmet, describing the neat conical profile of young fruiting bodies.

Within the fungal world it belongs to the wood-decaying saprotrophs of temperate forests, and its adnate gills with a decurrent tooth, obvious cross-veins and pink flush in maturity distinguish it from the grey-capped bonnets that grow on litter and needles.

Cap

The cap is 2–6 cm across, which is large for the genus. It begins conical or narrowly bell-shaped and expands to a broad bell or nearly flat cap that almost always retains a distinct central umbo. The surface is dry, smooth and dull grey-brown, greyish-buff or tan, paler towards the rim, and it is conspicuously radially grooved or wrinkled from the margin nearly to the centre as it matures. The colour is somewhat hygrophanous, fading to pale greyish-cream in dry weather.

Gills

The gills are adnate with a short decurrent tooth running onto the stipe apex, fairly distant, and white to greyish at first. With maturity they take on a distinct pale pink or flesh-coloured flush, a feature that helps confirm the species. Low cross-veins connect the gills near the cap flesh, giving a slightly wrinkled inter-gill surface.

Stipe

The stipe is 4–12 cm long and 2–5 mm thick, hollow, smooth, polished and markedly cartilaginous or tough — it will bend and twist before it breaks. It is grey to grey-brown, usually paler at the apex and darker below, and the base is often extended into a short rooting portion clothed in coarse white hairs where it enters the wood.

Flesh and spore print

The flesh is thin, pallid and tough, sometimes with a faintly mealy or rancid odour when crushed. No coloured latex is present. The spore print is white.

The Common Bonnet fruits on decaying hardwood — stumps, fallen trunks, large branches and, very frequently, buried roots and wood fragments, which is why it sometimes appears to be growing from bare soil or from a lawn where a tree has been felled. Oak, beech, birch, willow and fruit trees are all regularly used, and it occasionally appears on conifer wood.

It grows in loose to tight tufts of several fruiting bodies joined at the base, and is one of the most widely distributed fungi of the northern hemisphere, common throughout Europe, temperate Asia and North America. Its season is exceptionally long, running from spring through to early winter, and in mild maritime climates specimens can be found in almost any month.

This species is a saprotroph causing a white rot of deciduous wood, colonising both exposed stumps and buried woody debris. It is an effective coloniser of cut surfaces, which is why freshly felled stumps in parks and gardens often carry generous tufts within a couple of seasons.

Because the mycelium persists inside a stump for many years, the same stump commonly produces fruiting bodies season after season until the wood is exhausted. The long fruiting period and tough construction let the species release spores across a much wider window than most bonnets, taking advantage of mild spells in late autumn and early winter when few other gilled fungi are active.

Mycena inclinata is very similar in size and habit and shares hardwood stumps, especially oak, but has a cap margin fringed with distinct whitish teeth and a stipe that is white at the apex and grades through yellow-brown to rust-brown at the base, while M. galericulata keeps a fairly even grey-brown stipe. Mycena polygramma has a stiff, silvery-grey stipe finely grooved with longitudinal lines, and a smaller, more sharply conical cap.

Mycena haematopus fruits in similar tufts on hardwood but is wine-brown and releases dark red latex from a broken stipe. Mycena maculata is close in stature but develops reddish-brown spotting on cap and gills as it ages. Among larger fungi, young Pluteus species can look superficially similar on the same logs but have free gills that turn pink and give a pink spore print.