Scaly Webcap
Cortinarius pholideus
Also called shaggy webcap
A strikingly shaggy webcap covered in dark brown erect scales on both cap and stem, with violet-tinged young gills and a violaceous stem apex. It partners with birch on damp acid soils.
Overview
Scaly Webcap (Cortinarius pholideus) is one of the easiest webcaps to recognise in the field, which is a rare thing in a genus of more than a thousand look-alike species. Both the cap and the lower stem are clothed in dark brown, pointed, upturned scales, giving the whole fruitbody a bristly, almost Pholiota-like appearance that the species epithet refers to.
It belongs to subgenus Telamonia, the dry-capped webcaps, but stands apart from its plainer relatives through this dense scaliness combined with a surprising splash of colour: the young gills and the top of the stem are violet, contrasting with the earthy brown scales around them. As spores ripen the violet is overrun by cinnamon and rust.
As an ectomycorrhizal partner of birch on acid, peaty soils, it is a characteristic autumn fungus of northern birch woods, birch carr and moss-carpeted heathland, and one of the small number of Cortinarius species a beginner can learn to name reliably by sight.
How to identify it
Cap
Usually 3–8 cm across, convex then flattening with a broad umbo. The ground colour is greyish- to dark brown, but the surface is densely covered with darker brown, erect to recurved, pointed scales that are largest at the centre and thin out towards the margin. The margin often retains pale veil fibrils and is inrolled when young.
Gills
Adnate to slightly notched, moderately crowded, distinctly pale violet or lilac when young — a striking contrast with the brown cap — then dulling through clay and cinnamon to rusty brown as the spores mature. A pale cortina covers the gills in button stages and later leaves a rusty fibrillose zone on the stem.
Stipe
About 5–10 cm tall and 0.6–1.5 cm thick, cylindrical or slightly thickened at the base. Above the veil zone it is smooth and violet-tinted; below, it is banded and shaggy with the same dark brown recurved scales that cover the cap, arranged in irregular girdles. This two-zone stem is the single most diagnostic feature.
Flesh & spore print
The flesh is pale brownish, violaceous in the upper stem, with a mild earthy smell and no colour change of note when cut. The spore print is rusty brown, and the spores are broadly ellipsoid and warted.
Where and when it grows
Cortinarius pholideus grows with birch, occasionally with alder or in mixed stands including conifers, on damp, acid, humus-rich or peaty soils. It is typical of birch carr, mossy birch woodland, damp heaths with scattered trees and the boggy margins of woodland pools, and often fruits directly out of Sphagnum or thick moss cushions.
Fruitbodies appear singly, scattered or in small groups from late summer through autumn. The species is widespread across northern and central Europe, with a strongly boreal and northern-temperate character, and is also recorded from birch woodland in northern North America.
Ecological role
This is an ectomycorrhizal fungus of birch. The fungal mantle it forms around fine root tips greatly extends the effective absorbing surface of the tree, which matters especially on the waterlogged, nutrient-poor acid soils where birch carr develops. Nitrogen and phosphorus flow to the tree, carbon flows to the fungus.
Because the mycelium persists for many years, the same mossy hollows tend to produce fruitbodies annually. In peaty birch woodland the fungus is part of a dense underground fabric of ectomycorrhizal species that stabilises the soil, mediates decomposition of leaf litter, and links neighbouring trees through shared mycelial networks.
Similar species
The nearest confusion is with scaly Pholiota species such as Pholiota squarrosa, which are also densely scaly but grow in dense tufts on wood or at the base of living trunks, have a membranous ring rather than a cobwebby cortina, and produce a duller brown spore print. Cortinarius hemitrichus and C. flexipes share the birch habitat but their veil forms flat white fibrils and frosting rather than erect brown scales.
Inocybe species can look bristly but are radially fibrillose or splitting rather than truly scaly, have a clay- to snuff-brown spore print and never show violet gills. Among webcaps, Cortinarius bolaris has red-brown scales on a pale ground and lacks violet tints, so scale colour, ground colour and the presence of violet in the gills and stem apex separate them.