Pearly Webcap Identification Guide

First Impression and Setting

You meet the Pearly Webcap in autumn broadleaf woodland, usually on acid to neutral soil with birch, beech, oak or hazel overhead, often on a mossy bank or among sparse litter rather than in deep leaf drifts. The first impression is of a medium-sized, dry, silvery mushroom that seems to glow faintly against dark ground. It has none of the greasiness of a wax cap and none of the scaliness of a knight; the surface is silky, like brushed satin, and washed with a cool blue-lilac or pale violet that is strongest on young caps and on the stem.

Because Cortinarius is an enormous genus, the working method matters more than the first impression. Always collect the whole fruitbody, including the base, and always collect more than one age class if you can, because half of the useful characters are young-only and the other half are old-only.

Reading the Cap

The cap is 3-8 cm across, occasionally 10, starting bluntly conical or hemispherical and expanding to convex with a broad low umbo. The surface is dry, never viscid, covered in appressed silky fibrils that give a satin shine. Colour is whitish to pale silvery violet, sometimes distinctly blue-lilac when young and fresh; with age and sun the disc fades or discolours to pale ochre or buff while the margin holds the pale tone longest.

Run a finger over the surface. It should feel dry and smooth, and if the mushroom is young the margin will still carry white cobwebby veil fibrils. If the cap is slimy, or if it is coarsely scaly, or if it has a marginate rim of tissue at the stem base, you are elsewhere in the genus.

The Cortina and the Gills

The cortina is the family signature. In young specimens a fine web of pale silky threads runs from the cap margin to the stem, veiling the gills. It never forms a membranous skirt. As the cap expands the web tears, leaving a fibrillose zone on the upper stem, and as spores mature this zone catches them and turns a distinctive rust-brown. On a mature Webcap that rusty smear on the stem is often the easiest confirmation of genus at a glance.

The gills themselves change colour with the spore load, which is why age classes matter. Young gills are pale violaceous, greyish lilac or clay with a violet cast, moderately crowded, adnate to slightly notched at the stem. They pass through clay-buff to cinnamon and end up dull rust-brown, with paler minutely uneven edges. If your specimen has bright violet gills in youth, or ochre-brown gills from the very start, consider the alternatives listed below.

Stipe, Base and Flesh

The stipe is 5-10 cm long and 1-2 cm thick, firm, solid, and characteristically clavate: it thickens gradually downwards into a club or a swollen base without ever forming a sharp-edged marginate bulb. Colour matches the cap, whitish to pale lilac, overlaid with a silky white sheath of universal veil that may leave vague girdles or a faint fibrillose sock over the lower half. Above the ring zone the surface is often more strongly violet.

Slice the fruitbody lengthwise. The flesh is white to pale cream, tinted violaceous in the stem apex and in the cortex just under the cap skin, firm and solid rather than watery. There is no dramatic colour change on cutting or bruising; at most the base slowly discolours pale ochre. Nothing turns blue, nothing turns black, no latex appears. The odour is faint and mild, sometimes vaguely earthy, and the absence of a strong penetrating smell is itself a separating character.

Spore Print and Microscopy

Remove the stipe and lay the cap gill-side down on white paper for two to four hours under a cover. The print is rust-brown, warm and unmistakable once you have seen it beside the pinkish print of a Blewit. Rust-brown print plus a cobwebby cortina is effectively a definition of Cortinarius.

Under the microscope the spores are ellipsoid to broadly almond-shaped, 8-10.5 x 5-6.5 microns, and finely to moderately verrucose, that is covered in small warts rather than smooth. Smooth spores would take you out of the genus altogether.

Substrate, Season and Ecology

This is an ectomycorrhizal species, forming sheathing root associations with broadleaf trees, birch above all, but also beech, oak and hazel. It fruits from late summer into autumn, appearing in small scattered groups on mossy, humus-rich, often acidic ground under those hosts. It is not a wood-rotter, so a Webcap-looking mushroom growing directly from a log or stump needs a different name. Presence of the right host is genuine evidence, so always note the surrounding trees before you leave the spot.

Separating the Look-Alikes on Morphology

Cortinarius traganus is the classic confusion. It is stouter, more lilac-buff, grows with conifers, and gives itself away when cut: the flesh is a marbled ochre-brown rather than white with violet tints, the gills are ochre-brown from an early stage instead of violaceous, and the odour is strong and penetrating.

Cortinarius camphoratus also has a powerful smell and young gills of a much deeper, more saturated violet; it too is a conifer species.

Cortinarius malachius has a more fibrillose to slightly scaly cap surface and again favours conifers, with the violet tones fading faster.

Cortinarius anomalus and its relatives are smaller and greyish ochre-brown over the cap, retaining lilac only at the stem apex and in the young gills; the cap never has that silvery-white silky sheen.

Lepista nuda, the Wood Blewit, is the most common non-Cortinarius confusion. It has no cortina at any age, its gills stay lilac and never rust, its stem is streaked violaceous and fibrillose without a rusty ring zone, and the spore print is pale pink, not rust-brown.

Inocybe geophylla var. lilacina shares the lilac colour but is much smaller, with a sharply conical silky cap that often splits radially, no true cobwebby cortina, and a dull clay-brown print.

Field Checklist

Dry, silky, silvery lilac-white cap; young violaceous gills ageing rust; cobwebby cortina leaving a rust-dusted zone on a clubbed, pale violet, silky-sheathed stem; white flesh with violet tints and no colour change; rust-brown spore print; with broadleaf hosts in autumn.