White Fibrecap

White Fibrecap is a diminutive but abundant woodland agaric, instantly recognisable by its pure white, satin-sheened cap raised into a small sharp nipple at the centre. It belongs to Inocybe, a large genus of brown-spored, mycorrhizal fungi whose members typically have dry fibrous or silky caps and a distinctive earthy-spermatic odour.

The species is important as a benchmark for learners because whiteness is unusual in the genus: most fibrecaps are shades of brown, ochre or grey. Its silky white cap, brown-maturing gills and slender white stipe make an unusual combination that, once learned, is quickly picked out along shaded woodland tracks.

A lilac-tinted form growing alongside the typical white plants has long been treated as Inocybe geophylla var. lilacina and is now widely recognised as a separate species, Inocybe lilacina. Intermediate specimens with faintly violet-flushed caps that fade to cream are frequent, and the two frequently share the same patch of woodland floor.

Cap

Small, 1–3.5 cm across, conical then bell-shaped and finally almost flat but always retaining a distinct pointed umbo. The surface is ivory to pure white, dry, and finely silky-fibrillose with a noticeable satin or silken shine; older caps may develop a faint ochre or straw tint at the umbo. The margin may split slightly with age but never as coarsely as in the larger fibrecaps.

Gills

Adnexed and moderately crowded, whitish at first and then slowly turning grey-buff, clay and finally dull brown as the spores ripen. The edges remain whitish and minutely fringed. The colour change of the gills against the unchanged white cap is the single most useful feature for confirming an identification.

Stipe

Slender, 2–6 cm tall and only 2–5 mm thick, cylindrical with a slightly swollen but not rimmed base. It is white, silky-fibrillose and solid, sometimes with a very faint cobwebby veil at the apex when young that soon vanishes. There is no true ring.

Flesh and spore print

The flesh is thin and white, unchanging when cut. The odour is distinctly earthy or spermatic. The spore print is snuff-brown to dull clay, and the spores are smooth and almond-shaped rather than nodulose.

White Fibrecap grows on soil in deciduous, mixed and coniferous woodland, and is especially frequent along shaded path edges, banks, ditch sides and mossy verges where the leaf litter is thin. It is often gregarious, appearing in scattered troops of dozens of small fruitbodies at once, and tolerates a wide range of soils from sandy to calcareous.

The season runs from midsummer to late autumn, sometimes lingering into early winter in mild spells. It is common and widespread throughout Europe, North America and temperate Asia, and is one of the fibrecaps most likely to be found in urban parks and planted amenity woodland.

This is an ectomycorrhizal species, forming root partnerships with a wide range of trees including beech, oak, birch, hazel, willow, pine and spruce. Its hyphae ensheath the host's fine feeder roots and extend into the surrounding soil, supplying mineral nutrients and moisture in return for photosynthetic carbon. Being a generalist, it can associate with whichever suitable trees are present, which underpins its very wide distribution.

Because it fruits abundantly in disturbed marginal habitats, White Fibrecap is a useful indicator of active mycorrhizal networks in young woodland and planted landscaping. The small fruitbodies decay within a few days and are quickly consumed by fungus gnats, springtails and slugs.

Small white Mycena and Hemimycena species have a similar silhouette but keep white gills throughout and give a white spore print, never the snuff-brown of a fibrecap. Snowy Waxcap, Cuphophyllus virgineus, has a slightly greasy cap, thick waxy widely spaced gills that run down the stipe, and white spores.

The Miller, Clitopilus prunulus, is stockier with a matt, felted, often lobed cap, decurrent gills and a pink spore print. Inocybe lilacina is essentially identical in shape and structure but shows lilac to violet tones on cap and stipe when fresh, fading to buff, whereas true White Fibrecap is white from the start.