[5] French naturalist Jean-Baptiste Lamarck viewed it as a variety (violaceus) of a variable species he described as Amanita araneosa in 1783,[6] and Christiaan Hendrik Persoon placed it in the Section Cortinaria of Agaricus in his 1801 work Synopsis Methodica Fungorum.

[7] Cortinarius was established as a genus by English botanist Samuel Frederick Gray in the first volume of his 1821 work A Natural Arrangement of British Plants, where the species was recorded as Cortinaria violacea, "the violet curtain-stool".

[8] The starting date of fungal taxonomy had been set as 1 January 1821, to coincide with the date of the works of the "father of mycology", the Swedish naturalist Elias Magnus Fries, which meant the name Cortinarius violaceus required sanction by Fries (indicated in the name by a colon) to be considered valid.

[9] Hence, the name no longer requires the ratification of Fries's authority, and is thus written as Cortinarius violaceus (L.) Gray.

In 1891, his countryman Otto Kuntze published Revisio Generum Plantarum, his response to what he perceived as poor methodology in existing nomenclatural practice.

Because of this designation, if C. violaceus were to be split from the rest of the current genus, then, according to the rules of the International Code of Botanical Nomenclature, it would retain the name Cortinarius, while the other species would have to be reclassified.

[14] A 2015 genetic study by evolutionary biologist Emma Harrower and colleagues of C. violaceus and its closest relatives suggests that the group (section Cortinarius) originated in Australasia and began diverging from a common ancestor around twelve million years ago in the Miocene, with C. violaceus itself diverging from its closest relative around 3.9 million years ago.

The fact that these species diverged relatively recently indicates that some form of dispersal must have taken place across large bodies of water.

[16] Moser separated them once again as species in 1967, and Norwegian biologist Tor Erik Brandrud classified C. hercynicus as a subspecies of C. violaceus in 1983.

[14] Some fungal populations around the world that have been classified as C. violaceus have been found to belong to separate lineages and hence reclassified as new species within section Cortinarius.

[15] Two separate lineages discovered in populations from Costa Rica have been renamed Cortinarius palatinus and C. neotropicus,[18] one from Guyana—described as sp.

The stipe is a similar colour to the cap, and covered in wool-like fibrils;[4] purple mycelium can be present at the base.

[3] Cortinarius iodes of the southeastern United States has a slimy purple cap and paler violet stipe.

[23] The other species in the section Cortinarius are dark purple and superficially similar, but can be differentiated based on host and geography as they do not occur in the same locations as C. violaceus.

[14] Certain Leptonia species in northwestern North America, including L. carnea and L. nigroviolacea, have a similar color, but are easily differentiated due to their pink spore print.

[17] In Europe, it grows in deciduous woodland during autumn, especially among oak, birch and beech, but is also found on occasion with conifers.

hercynicus grew with Picea abies, generally in more alkaline soils and along with mosses of the genera Hylocomium and Pleurozium, and, in moister areas, big shaggy-moss (Rhytidiadelphus triquetrus), as well as the buttercup-family shrub Hepatica nobilis.

[17] The species grows with Betula pubescens in Greenland,[24] and is also associated with hazelnut (Corylus avellana) in Central and Southern Europe.

[13] It is more common in old growth forest in the Pacific Northwest, though has sprung up in regrowth areas populated with fir, pine, aspen and alder in the Great Lakes region.

[3] Fruit bodies occur singly or in small groups, often near rotting wood,[13] and can grow in fairy rings.

[27] Closely related species that look like C. violaceus can be found in Central and South America, Australia, New Zealand, Papua New Guinea, and Malaysia.