Grey Milkcap Identification Guide

Where You Will Be Standing

Grey Milkcap is a birch specialist of wet ground. The classic setting is a scruffy birch wood on acid soil in October: sphagnum and haircap moss between the trunks, a squelch underfoot, bilberry or heather at the edges, and drifts of curled birch leaves. The mushrooms are scattered rather than clustered, often half-buried in moss so that only a grey disc shows.

The first impression is of a modest, dull, greyish mushroom with a faintly slimy shine after rain and a slightly translucent, thin-fleshed look. Nothing about the colour is striking. What tells you immediately that you are in Lactarius or Russula is the texture: pick one and the stipe snaps cleanly, like a stick of chalk, with no fibrous stringiness. That brittleness comes from the rounded cells packed through the tissue of the Russulaceae, and it is the fastest genus test in the field.

Reading the Cap

Expect 3 to 8 cm across. The shape begins convex with an inrolled margin, flattens, and then becomes shallowly depressed to funnel-shaped, sometimes retaining a low central bump. The flesh is thin for the size of the cap, and the margin is often slightly wavy or lobed in mature specimens and may become faintly grooved.

Colour is a muted grey with a violaceous, lilac or dull brownish cast, generally darker in the centre and paler towards the rim. Wet caps look greasy to slightly sticky and slightly shiny; the same cap after a dry day is matt and can look almost powdery grey. Faint watery zoning near the margin is sometimes visible in fresh material but never the strong concentric bands of the zoned milkcaps. The surface is smooth, without scales, and the margin is bald, not shaggy or hairy.

Gills, Latex and the Key Colour Change

Turn the cap over. The gills are adnate to slightly decurrent, crowded, rather narrow, and pale cream to whitish, with some forking near the stipe and short intermediate gills. So far this describes a great many milkcaps. The identification hinges on what happens next.

Nick a gill or draw a knife tip across the cap flesh. Latex appears white and reasonably abundant in fresh, damp material, sparse and slow in dry weather, so collect after rain if you can. Now be patient. Smear a drop on a white handkerchief or a piece of paper, leave the cut gill undisturbed, and check both after five, ten and fifteen minutes. In Grey Milkcap the latex dries grey to greenish-grey, and the damaged gill tissue takes on distinct grey stains. Older fruit bodies show this without any help from you: look for grey blotching along the gill edges, at insect holes and wherever slugs have grazed.

That sequence, white latex drying grey with grey staining on a birch-associated, greasy grey-lilac cap, is the whole identification in a single observation.

Stipe, Base and Flesh

The stipe is 3 to 8 cm long and 6 to 12 mm thick, cylindrical or tapering slightly downward, pale grey-buff to nearly the colour of the cap but paler, smooth, and dry. Look carefully for pits: some milkcaps have scattered darker depressions, called scrobicules, and Grey Milkcap does not. The stipe becomes hollow with age and often develops a chambered interior; it snaps rather than tears.

The flesh is white to pale greyish, thin, and fragile, and it greys where damaged as the latex dries within it. Cut a stipe lengthwise and leave it face up in the collecting basket for a quarter of an hour to see this clearly. The smell is faint and unremarkable, sometimes very slightly fruity or of damp leaves, and is emphatically not a strong smell of coconut or of dried curry.

Taking a Spore Print

Set a mature cap gills down on white paper under a cup for four to eight hours; thin-fleshed caps dry out fast, so cover them properly. The deposit is pale cream, sometimes with the faintest buff tint, and it is easiest to judge by scraping the powder into a small heap with a blade and comparing it with the paper.

Under the microscope the spores are broadly ellipsoid, roughly 7 to 9 by 6 to 7 micrometres, and ornamented with amyloid ridges and warts that link into an almost complete network. A drop of Melzer reagent turns the ornamentation blue-black against a hyaline spore body, which is the standard Russulaceae confirmation.

Substrate and Season

Grey Milkcap is ectomycorrhizal and, in practice, restricted to birch. Search downy birch and silver birch on damp acidic ground: bog margins, wet heath, mossy birch scrub, poorly drained plantation edges and the birchy fringes of conifer blocks. It appears from late summer, peaks through autumn, and persists until hard frosts. Because the partnership is with living roots, productive spots repeat annually. Fruit bodies are usually scattered singly or in small loose groups among moss rather than in dense troops.

Separating the Look-Alikes on Morphology

Coconut Milkcap, Lactarius glyciosmus. Shares birch and damp ground exactly. It is smaller, drier and more finely velvety or pruinose, with a pinkish-grey to lilac-buff cap, more ochre-buff gills, and a strong, unmistakable smell of coconut. Its latex stays white on drying and does not stain the gills grey.

Lactarius uvidus. Larger and paler, with a distinctly slimy cap. Its latex turns lilac to violet within a minute or two, and the cut flesh and damaged gills flush violet rather than grey.

Lactarius trivialis. Much bigger, up to 15 cm, with a greasy grey-violet cap, chiefly in damp northern spruce and birch woodland. Its greater size and stout stipe separate it before any latex test.

Lactarius blennius. Latex also dries grey, but this is a beech associate with a thicker-fleshed, olive-grey cap decorated with concentric rings of darker droplet-like spots. Tree partner plus cap markings settle it.

Lactarius torminosus and Lactarius pubescens. Also under birch, but the cap is pinkish to salmon and the margin is conspicuously shaggy with coarse woolly hairs.

Lactarius circellatus. A hornbeam associate with a clearly zoned grey-brown cap and firmer flesh.

Lactarius fuliginosus and Lactarius azonites. Velvety, dry, greyish-brown caps whose white latex turns salmon-pink on the flesh instead of grey.

Russula and Mycena species. Grey Russula species have the same brittle snap but produce no latex at all; grey Mycena species are far smaller, with tough cartilaginous stems and thin membranous flesh. Always look for latex first.

Field Checklist

Birch, damp acid ground, autumn. Cap 3 to 8 cm, greasy when wet, grey with a lilac or brownish cast, depressed with age. Gills crowded, pale cream, greying where damaged. Latex white, drying grey to greenish-grey. Stipe pale, smooth, unpitted, soon hollow, brittle. Spore print pale cream with a ridged, netted, amyloid ornament. Odour faint and not of coconut.