Common Bonnet Identification Guide

The Encounter

Most finds begin the same way. You are walking through mixed deciduous woodland, you pass a mossy stump or a long-fallen trunk lying in leaf litter, and out of one split in the wood rises a tight bouquet of twenty or thirty small grey mushrooms. From two metres away the impression is entirely of shape: little bells or helmets on long, wiry, faintly polished stalks, all radiating outward from a single anchor point in the wood. Nothing about it is colourful. That greyness, that clustered habit, and the sheer length of stalk relative to cap size are the three things that should make you kneel down.

Lift the whole clump rather than plucking one fruitbody. Bonnets are identified as much by how they attach, how the base looks, and how they behave between your fingers as by any single measurement, and an intact cluster hands you the growth habit, the base, and the full age range of the colony in one go.

Reading the Cap

The cap of Mycena galericulata runs roughly 2 to 6 cm across, which makes it a giant among bonnets. Young ones are narrowly conical or bell-shaped; as they age the bell expands into a broad low dome that almost always keeps a distinct blunt umbo in the centre, so the profile in silhouette is a shallow tent with a raised peak rather than a smooth curve.

Colour is grey-brown, mouse grey, or a dull clay-buff, usually a little darker over the umbo and paler toward the rim. The surface is dry and matt, never sticky, and never scaly. Look at the margin against the light: you should see fine radial lines, the grooves that trace the gills beneath the thin cap flesh. In wet weather those lines run further toward the centre and the whole cap darkens; in dry weather it fades to a pale silvery grey and the grooves become shallow furrows. Older caps frequently split at the rim into a few radial tears, which is normal for the species and not a separate character.

The Gills: The Detail That Settles It

Turn the cap over. This is where the Common Bonnet gives itself away. The gills are moderately spaced, fairly broad, and attached to the stipe in a distinctive way: they run up to it and then usually push a short tooth a little way down it, so the attachment reads as adnate with a decurrent tooth rather than cleanly free or cleanly notched.

The colour sequence matters. Young gills are white to pale grey. With age they take on a definite flesh-pink or rosy-buff tint, which is unusual and useful, because it happens even though the spore deposit itself never becomes pink. Then, with a hand lens angled across the gill spaces, look for cross-connections: low veins and wrinkles running between neighbouring gills near the cap edge, so that the underside looks slightly webbed or netted rather than made of clean parallel plates. This intervenose gill surface is the single most quoted field character for the species, and on a mature specimen in good condition it is genuinely visible at ten times magnification.

Stipe and Base

The stipe is long — commonly 5 to 10 cm, sometimes more — and slender, 2 to 5 mm thick, equal along its length. It feels quite different from a typical small mushroom stalk: tough, elastic, almost cartilaginous, and it will bend a long way before it snaps. The surface is smooth and slightly polished, grey to grey-brown, usually paler and almost white toward the apex and darker below. There is no ring and no volva. Snap one and you will find it hollow.

The base is the part people skip and should not. Run your thumb over it: in this species the very bottom is typically clothed in coarse white or greyish hairs, and the stipes of a cluster often continue as a rooting extension down into a crack in the wood or into buried timber. If you dig gently, a specimen apparently growing on soil often turns out to be attached to a buried root or a fragment of old plank.

Flesh, Section and Smell

Slice a cap and stipe lengthwise. The cap flesh is thin, whitish to watery grey, and essentially the same colour as the surface. Nothing changes when you cut it, nothing exudes, and rubbing or bruising the gills produces no reddening, blueing, or blackening. That negative result is a real character in its own right, because several superficially similar wood bonnets do stain or bleed.

Smell a freshly broken stipe: the odour is faint and mealy, sometimes turning damp and slightly rancid in old clusters, and never strongly chemical or sharply nitrous.

Taking a Spore Print

Cut the stipe flush with the gills, lay the cap gill-side down on a slip of white paper or a glass slide, cover it with a cup to hold humidity, and leave it for two to four hours. Because the caps are thin and dry out fast, a Common Bonnet that has been in a warm pocket may drop nothing at all — pick a fresh mature cap, one that is fully expanded but not yet splitting, and print it the same day.

The deposit is white to very pale cream. Read it against both white and dark backgrounds; on white paper a thin layer of white spores is easy to miss, so tilt the sheet to the light. A white print, combined with clustered growth on wood and those veined pinkish gills, rules out a great many things at once.

Substrate and Season

This is a wood-rotting fungus of deciduous timber: oak, beech, birch and willow stumps, fallen trunks, sawn log piles, and buried roots. Conifer wood is a much rarer host. It is a decomposer working on the interior of stumps long after the bark has gone, and it fruits from the same stump for years in succession.

Its season is the longest of almost any bonnet. Fruitbodies appear from late spring through summer and peak in autumn, and in mild damp winters clusters will keep appearing on sheltered stumps well into December. If you are looking at a clustered grey bonnet on hardwood in June, or in January, this species is the first candidate simply on timing.

Sorting Out the Look-alikes

Clustered Bonnet (Mycena inclinata) is the closest match in habit, also forming dense clumps on oak. Separate it on two features: the cap margin is finely scalloped with small pale sterile teeth, and the lower stipe turns a strong yellow-orange to rust-brown while the top stays white, giving a two-tone stalk. Mycena galericulata has an evenly grey-brown stipe and an entire margin.

Grooved Bonnet (Mycena polygramma) grows singly or in small groups rather than tight clusters, and its stipe is stiff, silvery-grey, and marked with fine longitudinal grooves that catch the light like a bundle of wires. Its gills stay grey and do not develop the rosy tint or the strong cross-veining.

Burgundydrop Bonnet (Mycena haematopus) also clusters on hardwood and has a similar bell, but the cap is reddish-brown with a toothed margin, and a cut stipe releases a dark blood-red juice within seconds. If it bleeds, it is not the Common Bonnet.

Mycena maculata is very close indeed but develops distinct reddish-brown spots on the gills and cap with age and favours conifer wood in many regions.

Psathyrella piluliformis forms similar tufts on hardwood stumps, but its caps are date-brown and strongly hygrophanous with a fringed margin, its stipe is brittle and snaps like chalk, and its spore print is dark purplish-brown rather than white. The print alone settles it.

A Field Sequence That Works

Confirm the substrate is dead deciduous wood; confirm the clustered habit; check the cap is grey-brown, dry, striate and umbonate; check the stipe is long, smooth, tough and one colour; look with a lens for pinkish mature gills with cross-veins; cut to confirm no colour change and no latex; then print white. Run those seven steps in order and the Common Bonnet becomes one of the most reliably named small woodland fungi you will ever meet.