Greenfoot Fibrecap Identification Guide

The Setting

Think wet conifer forest. This species turns up from late summer into autumn on damp, mossy or peaty ground under spruce and pine, along stream sides, in the fringes of bog woodland where sphagnum runs up to the tree bases, and in northern birch and mixed woodland on permanently moist soil. It is mycorrhizal and fruits from the ground, usually singly or in small scattered groups rather than in troops. You are looking down into deep moss when you find it, and it is easy to miss because the cap is dark brown against dark ground.

First Impression

A small, dark, distinctly shaggy mushroom on a shaggy stem. Where most fibrecaps read as silky and streaked, this one reads as bristly: the cap and much of the stipe are covered with coarse, upturned, pointed scales that break the outline. The fruit body is not fleshy, the stipe is slim and the whole thing is dry to the touch. If you dig it out and clean the base, the identification usually makes itself, because the bottom centimetre is flushed an unexpected blue-green.

Cap in Detail

The cap is 2 to 5 cm across, conical to convex at first and expanding to broadly convex or flattened with a low umbo. The ground colour is dark brown, umber or chocolate, sometimes with reddish or blackish tones at the centre. The surface is dry and never viscid, and it is densely covered with coarse fibrillose scales that stand out or curve upwards, most crowded and most erect over the disc and becoming more appressed and radially arranged towards the margin. Between the scales the underlying surface is paler brown. The margin is inrolled when young, often ragged with fibrous veil remnants, and may split radially in older caps. A cap this dark and this squarrose is unusual in the genus and narrows the field immediately.

Gills, Edge and Attachment

Turn it over. The gills are adnexed to almost free, moderately crowded and moderately broad, pale grey to greyish-buff when young and darkening through dull ochre to olive-brown or clay-brown as the spores mature. The edge is paler and finely fringed under a lens. Older gills sometimes show scattered rusty or reddish-brown spotting, especially where insects have grazed them or where the fruit body has been handled, and this should be recorded as spotting rather than as a uniform colour change.

Stipe and the Green Base

The stipe is the best part of the fungus. It measures 3 to 8 cm long and only 3 to 8 mm thick, equal or very slightly thickened downwards, with no ring and no bulb. Along most of its length it is clothed in concentric bands of recurved, brownish, pointed scales, the same texture as the cap, which is what the species epithet, meaning curled, refers to. Above the scaly zone the apex is smoother and paler.

The base is the diagnostic character. In fresh material the lowest 5 to 15 mm is flushed blue-green to verdigris, sometimes an intense turquoise, sometimes only a dull greenish smudge. It may be hidden by soil and moss, so clean the base gently with a brush or a wet fingertip, and if you still see nothing, split the stipe lengthwise from top to bottom with a blade, since the colour is often stronger in the internal tissue of the base than on the surface. The pigment fades in old, dried or waterlogged specimens, so judge it on the freshest fruit body in the collection.

Flesh, Section and Odour

Sectioned lengthwise, the flesh is whitish to pale brownish in the cap and browner in the stipe cortex, with the green confined to the base. Many collections show reddish or wine-coloured tints developing in the stipe flesh after cutting, sometimes only faintly and sometimes strongly enough to be obvious within a few minutes, so make the cut and then look again after five minutes before writing your note. The odour is strong and distinctly unpleasant to most noses, variously described as pungent, rubbery or faintly fishy, and it is quite different from the sweet fruity smell of the green-capped fibrecaps.

Spore Print and Microscopy

Cut the cap free, place it gills down on white paper, cover it, and leave it for four to six hours. The deposit is dull brown to clay-brown, best judged as a thick scraped heap in daylight. Under the microscope the spores are smooth, without warts, angles or lobes, ellipsoid to slightly bean-shaped or reniform in profile, roughly 9 to 12.5 by 5 to 6.5 micrometres, which makes them noticeably larger than in many small fibrecaps. The gill cystidia are thin-walled and club-shaped, lacking the thick walls and crystalline apex found in a large part of the genus, and this pairing of smooth spores with thin-walled cystidia is why the species is now usually placed in Inosperma.

Substrate, Partners and Season

Record the trees. Spruce and pine are the classic partners, with birch in northern and montane sites, and the ground is characteristically wet: moss carpets, sphagnum edges, damp needle litter beside flushes and streams, and peaty banks. It is a soil fungus, forming mycorrhizal partnerships with those trees, and it does not fruit from stumps or logs. The season runs from mid or late summer into autumn, following rain, and in oceanic climates it can appear surprisingly early in the year on permanently damp ground.

Separating It From Look-alikes on Morphology Alone

Inocybe hystrix is the closest match on texture. It is similarly and dramatically squarrose, with erect scales on cap and stipe, but it is paler, greyer or more ochre-brown, has no green whatever in the base, and grows on rich, often calcareous soils under beech and hornbeam rather than in wet conifer ground. Splitting the stipe base settles it in seconds.

Inocybe lanuginosa is smaller and dark brown with a woolly-scaly cap, but its stipe is fibrillose to slightly scaly rather than boldly recurved-scaly, its base has no green, and its spores are covered in blunt nodules rather than being smooth, so a microscope separates them absolutely. Inocybe cincinnata is small, dark and fibrillose with lilac or violet tints at the stipe apex and no green base. Other dark brown fibrecaps in conifer woodland are generally silky-fibrillose rather than shaggy, and again lack any green.

Inocybe corydalina puts its green in a different place: the flush sits on a pale, umbonate, only finely scaly cap, the stipe base is pale and swollen without green, the odour is sweet and pear-like, and the habitat is broadleaf woodland on richer soil. If the green is on top, it is not this species.

Outside the genus, Pholiota squarrosa can look superficially similar in texture, being covered in dry upturned scales, but it is much larger, grows in dense clusters at the base of living or dead trunks rather than singly on soil, has a distinct ring zone on the stipe and a rusty-brown spore print, and never shows a green base. Any shaggy brown mushroom tufted on wood should be checked against that species first.

A Working Sequence

Wet conifer or birch ground; small dark brown cap with erect coarse scales; slim stipe scaly along its length; dig and clean the base and split it to look for blue-green pigment; note any slow reddening in the stipe flesh; register the strong unpleasant odour; take a dull brown spore print; confirm smooth, fairly large, bean-shaped spores. That sequence identifies the species without ever needing a chemical test.