Cortinarius
Cortinarius is a globally distributed genus of mushrooms in the family Cortinariaceae. It is suspected to be the largest genus of agarics, containing over 2,000 widespread species. A common feature among all species in the genus "Cortinarius" is that young specimens have a cortina (veil) between the cap and the stem, hence the name, meaning "curtained". Most of the fibres of the cortina are ephemeral and will leave no trace once gone, except for limited remnants on the stem or cap edge in some species. All have a rusty brown spore print. The common names cortinar and webcap refer  to members of the genus. Due to dangerous toxicity of several species (such as "Cortinarius orellanus") and the fact that it is difficult to distinguish between various species of the genus, non-expert consumption of mushrooms from the genus is discouraged. Distinguishing features. The veil protects the gills in younger specimens and usually disappears leaving little to no trace of itself as the mushroom grows. The spores of a "Cortinarius" mushroom are rust brown to brownish red in color. It is usually possible to identify a mushroom as being a member of the genus, but extremely difficult to positively identify  the species as many of the species are nearly identical. All mushrooms in this genus form mycorrhizae. Many mushrooms in the genus, for example "Cortinarius sanguineus" and other species in section "Dermocybe", are colourful and are often used for dyeing. Toxicity. Several mushrooms in the genus "Cortinarius" are poisonous, mainly because they cause acute tubulointerstitial nephritis. Some are even lethal, such as "Cortinarius rubellus" and "Cortinarius orellanus". Therefore, a common rule when it comes to mushrooms from this genus is that none of them should be eaten. Many Cortinarius varieties can be mistaken for other edible mushrooms (such as the  Blewit Mushroom) and should therefore be researched extensively before you consider ingesting a look alike of this genus. However, some species—notably the giant of the genus, "Cortinarius praestans" and the gypsy mushroom ("Cortinarius caperatus")—are edible and appreciated in several European countries. The toxin in "Cortinarius" species, orellanine is easy to detect because it is fluorescent. It has been found in at least 34 Cortinariaceae. Classification. Molecular studies of members of the genus "Rozites", including its most famous member "R. caperata", have shown them nested within "Cortinarius" and have been sunk into this genus. This genus was erected on the  basis of a double veil, yet its members do not form a discrete lineage and lie nested within "Cortinarius". Hence the genus is no longer recognised. Some consider the subgenus "Dermocybe" to have generic status. It does form a single lineage, but lies within "Cortinarius" so the consensus has been to sink it into the larger genus.