Lilac Bonnet Identification Guide

The Setting You Will Be Standing In

Most Lilac Bonnet finds start as a flicker of odd colour at the edge of your vision while you are looking at something else. The setting is damp temperate woodland in the second half of the year: a deep mattress of beech or oak leaves, or a compacted carpet of conifer needles, with mosses and rotting twigs woven through it. Scattered across that litter, singly or in loose troops of five or ten, are slender mushrooms on wire-thin stems. Most of them are grey, brown or bone-white. This one is not. Mycena pura carries a pink-lilac to violet wash that reads immediately as different, and it is noticeably larger and more solidly built than the average bonnet, so it sits at the point where a beginner starts wondering whether it is a Mycena at all.

Get down to ground level straight away. Almost the whole identification is done kneeling, with a hand lens and your nose.

Step One: Read the Overall Build

Before colour, read proportions. The cap is 2-5 cm across, occasionally a little more, sitting on a stipe 3-9 cm tall and only 2-6 mm thick. The whole fruitbody is fragile, but the stipe is cartilaginous and springy rather than soft and fleshy, and it is hollow when you split it lengthways. That combination of a small conical-to-flattened cap, a thin polished tubular stem and a litter habitat places you in the bonnet group before you look at a single microscopic character.

Step Two: The Cap

Start with shape. Young caps are bluntly conical to bell-shaped; they expand to broadly convex and finally to nearly flat, usually keeping a low, broad umbo in the middle. The margin is thin and, when the fruitbody is wet, translucent-striate: hold it against the light and you can see the lines of the gills through the flesh, radiating from the centre like the ribs of a tiny parasol.

The surface is smooth, slightly greasy when moist, matt when dry, and hygrophanous, which means the colour drains as it loses water. Colour is the trap. Classic material is lilac, rose-lilac or violet, deepest at the disc and paler towards the rim, but pale grey, ochre-brown, dull rose and almost white forms all occur and are all still within the species complex. Do not reject a candidate because it is the wrong shade; check the other characters and let the colour be supporting evidence rather than the verdict.

Step Three: The Gills

Turn the cap over. The gills are adnate, usually running onto the top of the stipe as a short decurrent tooth, and in fat specimens they can look faintly notched. They are moderately spaced rather than crowded, broad and distinctly ventricose (deeper in the middle than at either end), with two or three tiers of shorter lamellulae between them.

Now look with a lens at the spaces between the gills. In Mycena pura you will usually see transverse veins connecting neighbouring gills near the cap flesh, a low webbing between the blades. That interveining is a genuinely useful character. Colour runs from whitish through pale pink-lilac; critically, the gill edge is the same colour as the gill face. Take that reading carefully, because a dark gill edge sends you to a different species entirely.

Step Four: Stipe, Base and Flesh

The stipe is cylindrical and equal for its whole length, smooth and polished, often with a slight sheen, concolorous with the cap or a shade paler. It is hollow, and it snaps cleanly with a little click rather than tearing into fibres. At the very base there is a coarse tuft of white mycelial hairs binding leaf fragments and needles together, so lift the fruitbody by easing the litter away rather than plucking it, or you will leave that character behind.

The flesh is thin and watery, pale, and gives no colour change on cutting or bruising. There is no latex, no gel layer, no ring and no volva.

Step Five: The Smell

This is the step people skip, and it is the one that closes the identification. Crush a piece of the cap or stipe between finger and thumb, warm it in your palm for a few seconds, and smell it. Mycena pura is strongly raphanoid: a sharp, green, radish-like odour that is obvious even in a light breeze. A bonnet of this size and colour with a strong raphanoid odour is already at the door of the species.

Taking and Reading a Spore Print

The spore print is white. Because the caps are small and thin, use two or three of them. Cut the stipe flush with the gills, set the caps gill-side down on a sheet of glass or on paper that is half white and half black, cover them with a cup or a tub to hold humidity, and leave them somewhere still for a few hours or overnight. A white deposit is invisible on white paper until you tilt it to the light, which is why the half-and-half sheet or a glass slide is worth the trouble.

Under a microscope the spores are smooth, ellipsoid and roughly 6-9 by 3-4.5 microns, and they are amyloid: a drop of Melzer's reagent turns the mass grey-blue. The gill edge is lined with thin-walled, spindle- to club-shaped cheilocystidia. Amyloid spores plus a white print plus the field characters above is as far as anyone needs to go.

Substrate, Season and Ecology

Mycena pura is a litter decomposer. It works on fallen leaves, needles, small twigs and buried woody fragments rather than on standing timber, and it fruits from the litter surface rather than from an obvious piece of wood. It is happy under both broadleaves and conifers, on acid and neutral soils, and is common in beech, oak, birch, pine and spruce woodland as well as in shelterbelts and mature plantations. The season runs from early summer to late autumn with a strong peak in the cool damp weeks of September to November. It is widespread across Europe, North America and temperate Asia, and modern work treats it as a complex of closely similar species rather than a single tidy one.

Separating the Closest Look-alikes

Mycena rosea is the nearest relative and is stouter, with a cap that is a clear rose-pink rather than lilac, often flatter and larger, on a paler, thicker stipe. It shares the raphanoid odour, so odour will not split them; size, stature and pure pink versus violet tones will.

Mycena pelianthina is the one character check that must not be missed. It has the same size, litter habitat and raphanoid odour, but under a lens the gill edges are a dark purple-brown line against paler faces. If the edge is dark, you are not looking at Mycena pura.

Mycena diosma is greyer and more sombre lilac, fading quickly, with a complex odour rather than a clean raphanoid one.

Laccaria amethystina is violet throughout, but its gills are thick, widely spaced and waxy-looking, its stipe is fibrous and twisted rather than smooth and tubular, and it has no raphanoid odour. Its spores are globose and covered in spines.

Lilac fibrecaps such as Inocybe lilacina have a dry, silky, radially fibrillose cap, gills that mature to dull clay-brown, a spermatic odour and a clay-brown spore print.

Lepista and Cortinarius species with violet tones are bulkier: Lepista drops a pale pinkish print with warted spores, and Cortinarius shows a cobwebby cortina in youth and a rust-brown print.

Field Checklist

Small to medium bonnet, cap 2-5 cm with lilac to rose tones; translucent-striate margin when moist; broad, spaced, interveined gills with concolorous edges; hollow, polished, cartilaginous stipe with white basal hairs; strong raphanoid odour; white amyloid spore print; growing from leaf or needle litter in autumn woodland.