Bruising Webcap
Cortinarius purpurascens
Also called purple-staining cort, purplish cort
A robust webcap with a slimy streaky olive-brown cap whose violet gills and flesh flush deep purple wherever they are rubbed or cut.
Overview
The Bruising Webcap is a substantial, firm-fleshed mushroom from the Phlegmacium group of Cortinarius, the webcaps with viscid or slimy caps and dry stipes, usually with a swollen or rimmed bulb at the base. Where most of that group demands microscopy or chemical tests, this species offers an immediate field character: press a fingertip along the gills, and the violet deepens within moments to a rich purple stain.
It is a woodland fungus of moderately rich soils, appearing under both broadleaved and coniferous trees, and its stout build, marbled violet flesh and abruptly rimmed basal bulb give it a distinctly architectural look among the litter.
Colour is variable, from olive-brown through date-brown to strongly purple-flushed, particularly at the margin, and old sun-dried caps may lose most of their violet tones, so the bruising reaction remains the most dependable feature.
How to identify it
Cap
5-12 cm across, hemispherical then convex and finally flattened, with a margin that stays inrolled well into maturity. The surface is viscid to slimy when moist, drying shiny, and marked with fine radial fibrils that give a streaky appearance. Colour ranges from olive-brown and date-brown to reddish or purplish brown, often with violet tones near the margin and litter stuck to the slime.
Gills
Adnate to emarginate, crowded and fairly narrow, deep violet to bluish-violet when young and passing through clay to rusty brown as spores mature. Rubbed, damaged or insect-grazed gills flush conspicuously deep purple, and the reaction is quick and unmistakable.
Stipe
5-10 cm long and stout, violet to lilac and clothed in silky fibrils, ending in a swollen bulb that is often rimmed or marginate, with a distinct edge where the bulb flares. The cobwebby violet cortina leaves a rusty-dusted fibrillose zone. Handled areas of the stipe surface also darken purple.
Flesh & spore print
Flesh is thick, firm and pale violet, marbled darker violet in the stipe, and stains distinctly purple where cut or bruised. The spore print is rusty brown, with almond-shaped, coarsely warted spores.
Where and when it grows
This webcap grows in both broadleaved and coniferous woodland, most often with beech, oak, hornbeam and Norway spruce, and favours moderately rich, often calcareous or base-influenced soils rather than the acid peats preferred by many of its relatives. Fruitbodies appear singly or in scattered groups in leaf litter and needle duff, sometimes in arcs where the mycelium has advanced outward.
The season runs from late summer through autumn. It is widespread across Europe from the Mediterranean to Scandinavia, and is fairly frequent, though patchy, in Britain. Related populations occur through temperate and boreal North America in comparable mixed woodland.
Ecological role
Cortinarius purpurascens is ectomycorrhizal, forming sheathing root tips on beech, oak and spruce. The fungal mantle and Hartig net provide a controlled interface across which the tree obtains nitrogen, phosphorus and water gathered by a wide-ranging hyphal network, in exchange for sugars fixed in the canopy. Trees growing with such partners typically show improved drought tolerance and nutrient uptake.
The violet pigments and their rapid darkening on injury are the result of oxidation when damaged tissue meets air, a common defensive response in fungi that may deter grazing invertebrates by making wounded tissue less palatable to them. Colonies are perennial and can occupy the same patch of woodland floor for many years, fruiting when autumn rain follows a warm summer.
Similar species
Cortinarius glaucopus also has a viscid cap and a marginate bulb, but its cap is more olive-green to tawny, its gills are bluish only when very young, and it does not stain deep purple on handling. Cortinarius caerulescens is a brighter blue-violet species with a dry to slightly viscid cap and a marginate bulb, again without the strong bruising reaction.
Cortinarius violaceus is unmistakably darker, a deep blackish violet throughout with a dry scaly-woolly cap and no viscid layer. Large Cortinarius largus has a similar bulk and pale violet young gills but a paler clay-lilac cap and no marked purple staining.