Violet Webcap

Cortinarius is the largest genus of gilled fungi in the world, with well over a thousand described species, and all of them share two features: a cobwebby partial veil called a cortina that stretches from the cap margin to the stem in young specimens, and a rusty-brown spore print that stains that veil as the spores fall. Cortinarius violaceus is the type species of the genus and by common consent the easiest of them all to recognise.

Its distinction is colour and texture together. The cap is not merely purple but a deep, dark, almost blackish violet, and the surface is dry and finely woolly-scaly rather than smooth or slimy, giving it a matt, suede-like appearance quite unlike the glossy purples found elsewhere in the genus. The gills are the same dark violet when young and only gradually take on the rusty overlay of maturing spores, while the flesh is violet-tinged throughout.

Microscopically the species stands slightly apart from most webcaps in possessing distinctive sterile cells on the gill faces, and modern work often splits it into a broadleaf-associated Cortinarius violaceus in the strict sense and a conifer-associated segregate, Cortinarius hercynicus, with broader, more rounded spores. In the field the two are essentially indistinguishable apart from the trees around them.

Cap

5-15 cm across, convex with an inrolled margin when young, expanding to broadly convex or flat, often with a low umbo. The surface is dark violet to blackish-purple, dry, and covered in fine radiating fibrils that break up into small upturned woolly scales, especially toward the centre. It has a matt, velvety look and is never viscid.

Gills

Adnate to notched at the stem, moderately spaced, fairly broad, and a striking dark violet when fresh. As the spores ripen the faces become dusted with rusty brown, and old specimens can look purplish-brown or cinnamon overall. In young fruit bodies the gills are covered by a pale violet cortina, a cobweb-like veil that later collapses onto the stem as a fibrillose zone stained rust-brown by falling spores.

Stipe

6-16 cm tall and 1-2 cm thick, violet throughout, dry and fibrillose, usually thickening downward into a club-shaped or slightly bulbous base that is often clothed in violet mycelial down. The remains of the cortina show as a diffuse rusty band rather than a true membranous ring.

Flesh and spore print

The flesh is firm, pale violet to greyish-violet, often deeper in colour in the stem base, and may show a faint bluish tinge on cutting. The odour is mild, sometimes described as recalling cedarwood. The spore print is rusty brown, a decisive contrast with the violet surfaces.

The violet webcap grows on the ground in woodland, typically on damp, mossy, acidic soils rich in humus. In Europe it is found under beech, birch and oak as well as in spruce and pine forest; in North America it is frequent in coastal and montane conifer stands, especially with spruce, hemlock and fir, and also occurs with birch and aspen. Specimens found under broadleaf trees are usually assigned to Cortinarius violaceus proper, while conifer material is often referred to Cortinarius hercynicus.

Fruiting runs from late summer into autumn, usually appearing after sustained rain and continuing until the first frosts. The distribution is broadly circumboreal across Europe, northern Asia and North America, with the species tending to be scattered and local rather than abundant, and favouring older, undisturbed stands.

This is an ectomycorrhizal fungus. Its mycelium sheathes the fine root tips of its host tree, penetrating between the outer root cells to form the branched interface through which water and mineral nutrients pass to the tree in exchange for photosynthetic sugars. Webcaps as a group are important members of this guild in northern forests, and Cortinarius species are often among the most numerous ectomycorrhizal partners on a given root system.

The cortina itself is an adaptation for protecting developing gills; as the cap expands the delicate threads snap, and rusty spores accumulate on the collapsed remnants around the stem, which is why a rust-stained zone on an otherwise violet stem is such a useful field character. Fruit bodies are relatively long-lasting for a soft-fleshed agaric and are frequently mined by fungus-feeding insect larvae.

Cortinarius iodes and Cortinarius iodeoides of eastern North America are also purple, but their caps are distinctly slimy or viscid, usually spotted or streaked with yellowish patches, and their flesh is whitish rather than violet. Cortinarius purpurascens has a viscid, brownish to purplish cap and flesh that stains deeper purple where bruised, and its stem base is abruptly rimmed and bulbous. Cortinarius traganus is pale lilac to greyish-violet with an ochre-brown flesh colour inside the stem and a strong sweetish odour.

Laccaria amethystina is a far smaller purple mushroom with thick, widely spaced, mealy-looking gills and, crucially, a white spore print with no cortina at all. Any dark violet mushroom with a dry felty cap, violet flesh, a cobwebby veil and rusty spores can be placed here with confidence.