When the cap expands, the threads stick to the stem, where the falling spores soon color this ring of threads reddish-brown. This makes the genus easy to recognize.
Identifying the species is another matter. There are close to one thousand species, some of which are quite large. And unlike other groups of conspicuous living things in the temperate world, many Cortinarius mushrooms have never been characterized and named by science.
Because the group is so large, it might take more than one lifetime to completely study, categorize, and name all these mushrooms. But since scientific interest and funds today focus on biotechnology, not biodiversity, this has not happened yet.
Toxicity
When I first began learning about mushrooms in 1980, some Cortinarius mushrooms were edible, others were poisonous. The poisonous ones were slightly toxic to the kidneys. But the kidneys removed the poison from the bloodstream. Unfortunately, instead of excreting the toxin in the urine, the kidneys return the poison to the blood, enduring an unnoticeably small amount of damage that doesn't manifest itself for several weeks, when kidney failure ensues!
Since then, there's been evidence that all Cortinarius species might have some of this toxin, so even the ones that people had been eating without obvious ill effects are suspect. Because of possible fatal kidney damage, because many of the species are so difficult to identify, and because many of the species are still unknown, you should avoid eating all Cortinarius mushrooms.
Ecology and Habitat
These mushrooms grown on the ground in coniferous and hardwood forests, where they exchange nutrients with trees. They're very common in the summer and the fall.
