Lilac Fibrecap Identification Guide

The First Impression

You usually meet the Lilac Fibrecap on bare ground rather than in deep litter. The typical setting is the compacted margin of a woodland track, a mossy bank under conifers, the trampled soil at the base of a bank of beeches, a path through dune scrub, or the thin turf beside a forest ride. It grows in small scattered troops, and the first impression is of a modest, tidy little mushroom, 1-3 cm across, standing upright on a slim stem, with a silky sheen and a soft violet or lilac cast that fades to buff and cream as it ages. Older specimens in the same troop may have lost the lilac altogether, so always search out the youngest fruitbodies in the group before deciding what colour you are dealing with.

A fibrecap identification is a sequence rather than a snapshot: cap texture, gill colour change, stipe surface, odour, spore print. Work through it in that order.

Step One: The Cap

The cap is small, 1-4 cm, and its shape is characteristic. It starts conical to bell-shaped, then expands to convex or nearly flat while keeping a persistent pointed or bluntly rounded umbo in the centre. That umbo is often a shade darker and more ochre than the rest.

The surface is the key texture. It is dry, never sticky, and covered with fine radial fibres pressed flat against the flesh, giving a silky, combed or brushed look under a lens. As the cap expands, those fibres separate, and the margin often splits radially, sometimes turning up. Colour in fresh young material is a soft lilac, pale violet or greyish-violet, warming to ochre at the umbo, and bleaching towards cream or dirty white in age or in sun. There is no gelatinous layer, no zoning and no scales beyond fine appressed fibrils. Occasional very young caps carry wispy pale veil fibrils along the margin.

Step Two: The Gills

The gills are adnexed, narrowly attached, sometimes almost free, and moderately crowded. Their colour sequence is the second key. When young they are pale greyish, often with a faint lilac tint; then they turn a dull clay or argillaceous shade; and in mature material they are a flat, dull cinnamon-brown. The important negative is that they never become rust-orange, never become chocolate, and never stay white.

Under a hand lens the gill edge looks paler than the face and finely fringed or frosted, because it is lined with cystidia. That whitish fimbriate edge against a browning face is a good supporting character.

Step Three: The Stipe, Base and Flesh

The stipe is 2-5 cm tall and 2-5 mm thick, roughly equal, sometimes very slightly swollen at the very bottom but without a sharply rimmed bulb. It is lilac in fresh young material, especially in the upper half, and fades pale buff. The surface is silky and longitudinally fibrillose along most of its length, with a fine powdery frosting (pruina) confined to the top third; check that with a lens against the light, because the extent of the pruina is a standard character in the genus.

Split the stipe. The flesh is whitish, sometimes with a violet tint in the outer layer, and it does not change colour on exposure. There is no ring, no volva and no latex. Now crush a fragment and smell it: the odour is strong, earthy and spermatic, a slightly acrid, animal smell that is typical of the genus and is one of the reasons a fibrecap can be picked out blind.

Taking and Reading a Spore Print

Set a mature cap gill-side down on white paper, cover it with a tub or cup, and leave it in a still place for two to six hours. The caps are small and the deposit will be thin, so use several and scrape the print together with a blade to judge the colour properly in daylight.

The print is a dull clay-brown, sometimes described as snuff-brown or tobacco-brown, with no rusty or orange tone and no purple-black tone. That reading alone eliminates a very large number of candidates in one move.

If you have a microscope, the confirmation is decisive. Spores are smooth, ellipsoid to slightly almond-shaped, about 7.5-10 by 4.5-6 microns, without nodules or bumps. On the gill face you should find pleurocystidia that are thick-walled and crowned with a cap of crystals at the apex; these are the metuloids that define the core of the genus. A smooth-spored fibrecap with metuloids, a lilac cap and a spermatic odour is Inocybe lilacina.

Substrate, Season and Ecology

This is an ectomycorrhizal species. It forms sheathing root partnerships with trees, and although it is often listed with conifers it is broad in its associations and turns up with pine, spruce, birch, beech, oak and planted broadleaves. It prefers well-drained, often disturbed or compacted mineral soil, which is why path edges, track sides, banks, dune slacks and the gravelly margins of forest roads are such productive places to search. Fruiting runs from midsummer to late autumn, typically July to November, and troops often reappear in the same few square metres each year because the underlying root partnership is perennial.

Because it is mycorrhizal, the presence of a host tree is part of the identification. A fibrecap of this description in a treeless lawn far from any woody plant should make you look again.

Separating the Closest Look-alikes

Inocybe geophylla is the white counterpart, identical in stature, texture, odour and microscopy, differing only in the absence of lilac pigment. Faded Lilac Fibrecaps and white fibrecaps growing side by side can be inseparable in the field, which is why you look for the youngest caps in the troop.

Inocybe cincinnata also carries violet tones, but the violet is restricted to the stipe apex and the young gills, while the cap is brown and more coarsely fibrillose to slightly scaly at the centre.

Mycena pura is the classic confusion. It has lilac tones and can be a similar size, but its cap is smooth and translucent-striate rather than dry and silky-fibrillose, its stipe is hollow, polished and cartilaginous, its gills are broad and interveined and stay pale, it smells raphanoid rather than spermatic, and its spore print is white.

Laccaria amethystina is deeper violet, with thick, widely spaced, waxy-looking gills that remain violet, a tough fibrous twisted stipe and a white print.

Cortinarius species such as Cortinarius alboviolaceus can be silky and violet, but they are larger, show a cobwebby cortina between cap margin and stipe when young, often leave a rusty band on the stem, and drop a rust-brown print.

Hebeloma species are larger, with slimy caps, a raphanoid odour, gills that weep droplets in humid weather, and no lilac tones.

Lepista sordida is much bigger and fleshier, with a smooth non-fibrillose cap and a pale pinkish print.

Field Checklist

Small dry cap with pressed radial fibres and a persistent umbo; lilac tones strongest in the youngest specimens; gills grey-lilac then clay then dull cinnamon with a pale fringed edge; slender lilac stipe pruinose only in the upper third; strong spermatic odour; dull clay-brown spore print; on bare or compacted soil beside paths under mycorrhizal trees, midsummer to late autumn.