Torn Fibrecap Identification Guide

First impression and the ground beneath you

Almost every Torn Fibrecap I have met has come off bare, impoverished ground: the compacted edge of a forestry track, a sandy path threading through birch scrub, the gravel margin of a car park cut into a pine plantation, or the mossy hollows behind coastal dunes. It is a small, dull, unglamorous mushroom, 1.5 to 4 cm across, and the first impression is of something dry and shaggy rather than smooth and polished. Against pale grit it reads simply as a dark brown scruff at ankle height. Where one appears there are usually several more, scattered rather than tufted, half sunk in moss or thin turf and often sharing the ground with young birch or pine.

The genus impression comes first and does most of the work. Fibrecaps as a group are dry, radially fibrous, dull brown or grey mushrooms with a conical or knobbed profile, a stem without a proper ring, and a dull brown spore deposit. Torn Fibrecap sits at the shaggiest end of that spectrum. Place the mushroom in the genus and the species characters follow quickly, and unusually for a fibrecap this one carries a microscopic feature so distinctive that a single glance down a microscope settles the question.

Working through the cap

Start with the profile. Young caps are bluntly conical to bell shaped, expanding to broadly convex with a low central umbo. The margin stays incurved for a long time and often carries remnants of a pale cortina, the fine web of veil fibres that hangs from the rim like torn cobweb and gives the species its English name.

The surface texture is the key character. Instead of the smooth radial silk of many fibrecaps, this one is coarsely fibrillose to distinctly scaly: the fibres lift and separate into small recurved scales, densest over the disc and shaggier towards the rim, so the cap looks combed and then ripped. Colour runs from mid brown through greyish brown to dark cigar brown, usually darkest at the centre, and the paler flesh showing between separated fibres gives a two tone effect. There is no viscidity whatsoever. Even in soaking weather the cap stays dry, and sand grains stick to it.

Gills, stipe and base

Turn the mushroom over. The gills are adnexed to almost free, moderately crowded, and pale grey or clay coloured when young, darkening to a dull earth brown or snuff brown as the spores ripen. The edges remain conspicuously paler, a fine whitish fringe visible with a hand lens, which is a reliable genus level confirmation.

The stipe is 2 to 5 cm long, slender and more or less equal, sometimes slightly thickened below but never ending in an abrupt rimmed bulb. It is coloured like the cap or a shade paler, clothed in longitudinal brown fibrils over a paler ground, and frequently shows a vague pale fibrillose zone near the top where the cortina tore away. There is no membranous ring. The extreme apex may be finely powdery under a lens. The base is simply tapered or slightly rooting and is usually bound to sand grains and moss, so lever the whole thing out with a knife rather than pulling: base shape matters throughout this genus and a snapped stem throws away evidence.

Flesh, odour and colour change

Split a specimen lengthwise through cap and stem. The flesh is thin, whitish to pale buff in the cap and browner in the stem cortex, firm rather than brittle. Colour change is minimal. Cut surfaces may dull slightly or go a shade browner over several minutes, but there is no dramatic reddening, blueing or yellowing, and the absence of a sharp reaction is itself useful, because several superficially similar brown mushrooms of the same habitat do react.

Odour is a legitimate field character here. Crush a fragment of flesh between finger and thumb and you should pick up the sharp, slightly spermatic or mealy smell typical of the genus, faint in dried out specimens and obvious in fresh damp ones.

Taking and reading the spore print

Cut the stem flush with the gills, set the cap gill side down on white paper or a glass slide, cover it with a cup or box to still the air, and leave it two to four hours somewhere cool. A young cap that has just flattened gives the heaviest deposit; a collapsing old one gives a smear. The print is dull clay brown to snuff or tobacco brown, with no rust, cinnamon or purple tone. That colour is exactly what separates fibrecaps as a group from rustgills, webcaps and brittlestems.

With a lens or microscope this species becomes unmistakable. Its spores are smooth, thick walled and remarkably long and narrowly cylindrical, far more elongate than the almond shaped spores of most smooth spored fibrecaps and never knobbly or angular. Add the thick walled cystidia on the gill faces and you have a clean, single character confirmation.

Substrate and season

The species is ectomycorrhizal, partnering mainly with pine and birch and less often with willow, spruce and oak. It therefore appears where those trees grow on thin, disturbed, sandy or gravelly ground: plantation rides, heaths, dune systems, quarry floors, spoil heaps and roadside verges cut into sand. It avoids deep rich leaf litter. The season is long, from early summer through to late autumn, and it is one of the fibrecaps most likely to be out in a dry August, because its habitats drain fast and it fruits on whatever rain does fall.

Separating the closest look-alikes

The split fibrecaps around Inocybe rimosa have sharply conical, strongly umbonate caps in ochre to straw brown whose radial fibres split into deep cracks running from margin to centre. Those fibres stay flat and silky rather than lifting into scales, so the cap looks polished and cracked rather than ragged and shaggy.

White Fibrecap, Inocybe geophylla, is smaller and silky white or lilac tinted, with a smooth conical cap and a slender white stem. Nothing about it is brown or torn.

Turnip Fibrecap, Inocybe napipes, shares the dark brown fibrillose cap but terminates in a distinct rimmed bulb like a small turnip, and its spores are angular and knobbed rather than smooth cylinders.

Scurfy Twiglet, Tubaria furfuracea, haunts the same paths but grows on woodchip and buried twigs, is strongly hygrophanous, fading from tan to buff in bands as it dries, has broadly attached to slightly decurrent gills, and drops a paler ochre brown print.

Hebeloma species can match it for size and colour but have smooth, slightly greasy caps with no shaggy fibres, and in humid weather their gill edges weep tiny droplets that dry as brown spots.

Finally, the deceivers, Laccaria species, share the sandy path habitat but have thick, widely spaced, waxy pinkish gills, a twisted fibrous stem and a white spore deposit, so the print alone separates them.