White Fibrecap Identification Guide

The setting and the first impression

The White Fibrecap is a woodland mushroom, and that context is worth fixing in mind before anything else. You find it on bare or mossy soil under trees: along the trodden edge of a path, on a bank beside a forest track, in leaf litter under beech, oak, birch, hazel or lime, and equally often under spruce and pine. It is scattered rather than clustered, and there are usually a handful in view once you have your eye in.

The first impression is of a small, neat, gleaming white mushroom, 3 to 6 cm tall, standing very upright with a sharply pointed cap. The word most collectors reach for is silky. Held against low light the cap has a satin sheen, and the whole fruitbody looks dry and finely fibrous rather than smooth or greasy. It looks tidier and more rigid than a bonnet, and smaller and sharper than most white woodland agarics.

Reading the cap

The cap is 1 to 3 cm across. Young caps are sharply conical, almost a cone with straight sides; they expand to bell-shaped and finally broadly convex, but they retain a pronounced, often nipple-like central umbo at every stage. That persistent sharp umbo is one of the most useful shape characters.

The colour is white to ivory or faintly cream, sometimes ageing to a dull straw or pale ochre tint over the umbo. The lilac form of the same species is coloured pale violet to lilac-grey and fades to nearly white in age, so a wash of lilac does not exclude it.

The surface texture is the genus signature. Under a lens, and often with the naked eye, the cap is covered in fine radial fibrils running from the umbo to the margin like combed silk. As the cap expands these fibres pull apart, so mature caps commonly split radially from the margin inward, sometimes deeply. There is no viscidity, no true scaliness, and no radial line pattern from the gills showing through.

Reading the gills

The gills are narrowly attached to the stem, sometimes appearing almost free, and are moderately crowded and rather narrow. Colour is the character that most quickly steers you away from the white-spored genera: they begin whitish to pale grey, pass through a dull clay or greyish-buff, and end a distinctly dull brown, often described as snuff-brown or cigar-brown, sometimes with an olive undertone.

Under a lens the gill edges are noticeably paler than the faces and minutely fringed with white. Line up a young and an old cap side by side to see the full sequence, because a single young specimen with pale gills tells you very little.

Stipe, base and veil

The stem is 2 to 6 cm long and 2 to 5 mm thick, white, more or less equal in width, solid rather than hollow, and finely silky-fibrillose over its length. At the very apex it is often finely pruinose, visible as a frosted dusting under a lens.

The base is at most slightly swollen or clavate. It is not marginate, that is, there is no abrupt rim or disc at the bottom, and there is never a sac, cup or membranous collar. Excavate the whole base out of the soil to check, since the swelling can be underground.

Young caps sometimes have a fine cobwebby cortina running from the cap margin to the stem, which vanishes quickly and may leave only a faint fibrillose zone or a few silky threads on the upper stem. There is never a persistent membranous ring.

Flesh, colour change and odour

Section the fruitbody lengthwise. The flesh is thin, white, and unchanging: no reddening, no blueing, no yellowing, no latex. That negative result is genuinely useful, because several of the pale woodland agarics it resembles do stain.

Odour is a legitimate field character here and worth using. Crush a piece of the cap flesh between finger and thumb and smell it immediately: the White Fibrecap has a strong, distinctive odour usually described as spermatic, or as earthy and slightly mealy. It is unmistakable once learned and is quite unlike the sweet or radish-like smells of most look-alikes, though the miller has its own strong mealy odour and needs separating on gill attachment instead.

Taking and reading the spore print

This species is small and the cap dries quickly, so use a fresh, fully expanded specimen and work promptly. Cut the cap free at the stem apex, lay it gills down on a glass slide, a strip of glossy white card or a piece of white paper, and cover it with a small glass to keep it humid. Two to four hours is usually plenty; overnight in a cool place is fine.

The deposit is dull clay-brown to snuff-brown, sometimes with a faint olive or greyish cast. Scrape it into a heap before judging the colour, because a thin scatter of brown spores can read as grey. Two negatives are as informative as the positive result: it is not white, which eliminates the waxcaps, bonnets and their allies, and it is not pink, which eliminates the miller and the pinkgills. It is also duller and less rusty-orange than the print of a webcap.

Substrate and season

The White Fibrecap is ectomycorrhizal, forming sheathing root partnerships with a wide range of trees. In practice that means you should only expect it in the presence of trees or shrubs: broadleaf woodland, conifer plantation, mixed parkland, hedge banks, or a wooded verge. It grows directly on soil, often in moss or thin litter and very often on compacted ground beside paths, where the mineral soil is exposed.

It is one of the most common and widespread small woodland agarics across the temperate northern hemisphere, and it fruits abundantly from mid-summer to late autumn, peaking in the same damp spells that produce the main woodland flushes.

Separating it from its closest look-alikes

Other fibrecaps. The genus is large and many species need microscopy to name, but the combination of a pure white to ivory, silky, sharply umbonate cap of 1 to 3 cm on a slender white stem is characteristic. The larger, more common brown fibrecaps such as the split fibrecap group are ochre to tan, 3 to 8 cm across, and split much more coarsely.

Snowy waxcap and its allies (Cuphophyllus virgineus and relatives). Grassland rather than woodland, with thick, waxy, distinctly decurrent gills that run down the stem, a greasy feel when moist, and a white spore print. The White Fibrecap has narrow, ascending to narrowly attached, dull brown gills and a dry silky cap.

Bonnets (Mycena). More fragile, with a translucent cap that is finely lined at the margin, a hollow wiry stem, white gills at all ages and a white spore print.

The miller (Clitopilus prunulus). Also strongly mealy-smelling, but the cap is matt, greyish-white, often lopsided and shallowly funnelled, the gills run distinctly down the stem, and the spore print is salmon-pink.

Small dapperlings (Lepiota). Free gills, a distinct ring or ring zone on the stem, scaly or granular cap surfaces, and a white spore print.

Webcaps (Cortinarius). Share the cobwebby cortina and brown mature gills, but are typically larger and more robust and drop a decidedly rust-brown print rather than a dull clay-brown one.

Pinkgills (Entoloma). Some are pale and umbonate, but their mature gills flush salmon-pink and their spore print is pink.

Field checklist

1. Woodland or wooded verge, on soil under trees, summer to late autumn.
2. Cap 1 to 3 cm, white to ivory, silky with radial fibrils, sharply umbonate, often splitting at the margin.
3. Gills narrowly attached, whitish then dull clay to snuff-brown, with paler fringed edges.
4. Stem white, silky, solid, equal, base at most slightly swollen and never marginate or sheathed.
5. Fleeting cortina at most; no membranous ring.
6. Flesh white and unchanging; odour strongly spermatic to earthy-mealy.
7. Spore print dull clay-brown, neither white nor pink.