Viscid Violet Cort

Viscid Violet Cort (Cortinarius iodes) is one of the most attractive webcaps of eastern North America. Fresh caps are a deep, glossy purple-violet, slick with a clear gluten that makes them shine in the humid summer woods where they appear, and as they age they become mottled with buff to yellowish spots and radial streaks — the feature that gives the species its second common name.

It belongs to the group of webcaps with glutinous caps and stems (subgenus Myxacium), and unlike the many dry violet species it feels distinctly slimy to the touch in fresh condition. The violet pigment resides in the cap surface and young gills; the flesh beneath is mostly whitish with a violaceous wash.

The species is a warm-season oak associate, fruiting in the summer and early autumn rains of the eastern deciduous forest. That timing is unusual for a genus dominated by cool-autumn species, and combined with its colour it is one of the more distinctive North American Cortinarius.

Cap

Typically 2–6 cm across, convex to broadly convex and often retaining a low umbo. The surface is smooth and conspicuously glutinous when fresh, coloured deep purple to violet, becoming paler and duller with age and developing scattered ochre, buff or yellowish spots and radial streaks, especially over the disc.

Gills

Adnate to slightly notched, moderately crowded, pale violet or lavender when young, then dulling to greyish-lilac and finally to a rich rusty cinnamon as spores mature. A pale cortina spans the cap margin and stem in buttons and leaves a rusty fibrillose zone behind.

Stipe

4–9 cm tall and 0.6–1.5 cm thick, cylindrical to slightly clavate at the base, whitish to pale violet and sheathed in a viscid to glutinous veil that dries slightly sticky. The apex is often the most strongly violet part of the stem.

Flesh & spore print

The flesh is whitish, tinged violaceous under the cap cuticle and in the stem apex, with a mild, indistinct smell and no strong bruising change. The spore print is rusty brown; spores are ellipsoid to almond-shaped and warted, a standard Cortinarius pattern.

Cortinarius iodes grows on the ground in deciduous and mixed forest, associating principally with oaks and also with beech and other hardwoods. It is found in leaf litter on well-drained slopes and along woodland paths, appearing singly, scattered or in small groups.

Its season is comparatively early for a webcap, running from midsummer through early autumn during humid, rainy spells. The species is characteristic of eastern North America, from the southeastern states north into the Great Lakes region and southern Canada, wherever oak-dominated hardwood forest occurs.

This is an ectomycorrhizal fungus of oaks and related hardwoods. The mycelium forms sheathed short roots and an extensive extramatrical network that scavenges nitrogen, phosphorus and water from litter and mineral soil, exchanging them for sugars produced by the tree canopy above.

The glutinous coating on cap and stem is a shared feature of the Myxacium webcaps and helps the fruitbody resist desiccation during the hot, humid conditions in which it fruits, as well as deterring some small grazers. Because the underground mycelium is long-lived, the same oak stands typically produce fruitbodies year after year, and the fungus forms part of the dense mycorrhizal community that underpins eastern deciduous forest.

Cortinarius iodeoides is the closest relative and is essentially a smaller, more slender version with a persistently slimy cap; the two are separated reliably only by size, slime persistence and microscopic characters. Cortinarius violaceus is superficially similar in colour but is much larger, dark violet throughout, and has a dry, coarsely scaly-fibrillose cap with no gluten at all.

Cortinarius alboviolaceus is a paler silvery-lilac species with a dry silky cap and a swollen stem base, while purple Laccaria species have thick, widely spaced gills and a white spore print. The combination of a slimy violet cap with yellowish spotting, a viscid stem and a rusty brown spore print is diagnostic.