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Cortinarius species

Webcaps · Deadly webcap · Fool's webcap

Deadly

A very large genus of brown mushrooms, a few members of which contain orellanine and can cause kidney failure days to weeks later, often permanently. All have a cortina, a cobwebby partial veil, and a rusty spore print. The genus is a good reason to treat 'small brown mushroom with a rusty print' as a hard stop.

Cortinarius rubellus, the deadly webcap, on conifer needle litter: a pointed tawny-brown cap, rust-brown gills and a yellowish stem with faint orange veil bands.
Photo: Matthew Rozanoff, CC BY, source.

If you may have eaten this: get to an emergency department now and say you may have eaten a webcap (Cortinarius), which can contain orellanine, a kidney toxin. Don’t wait for symptoms: they usually take days and can take up to three weeks, and that symptom-free stretch is part of the poisoning, not a sign you’re fine. Bring a sample if you can, and tell any doctor who later finds kidney problems about the meal.

What it does

Toxin
Orellanine, a kidney toxin, in C. rubellus, C. orellanus and a few related webcaps. Not an amatoxin: it damages the kidney tubules rather than the liver. There is no antidote; treatment is supportive, with dialysis.
Time to symptoms
The longest delay of any mushroom poisoning: 3 to 20 days before symptoms in one clinical series. Stomach upset often comes first (median about 3 days after the meal), then thirst and signs of kidney failure (median about 8.5 days).
Outcome
Acute kidney failure, often needing dialysis. In a review of 90 well-documented cases, about half progressed to chronic kidney failure, and most of those went on to need long-term dialysis or a transplant. The delay is so long that people rarely connect the illness to the meal.

Decisive characters

Each of these settles the question on its own. If one says no, the answer is no, regardless of what everything else says.

Spore print
Psilocybin speciesDark purple-brown
Look-alikeRusty brown, always
Bruising
Psilocybin speciesBlue
Look-alikeNo blue reaction

Supporting characters

Useful corroboration. Not sufficient alone.

Cortina
Psilocybin speciesAbsent, or a fibrous veil in a few species
Look-alikeA cobwebby veil between cap margin and stem in young specimens, leaving a rusty fibrous zone on the stem

Confused with

Other look-alikes to know

Other mushrooms that get mistaken for the same psilocybin species. Learn the decisive characters for each, and see the full look-alikes guide.

Sources

  1. [1]Danel, Saviuc & Garon, 'Main features of Cortinarius spp. poisoning: a literature review' (2001)
  2. [2]Frank et al., 'Acute renal failure by ingestion of Cortinarius species confounded with psychoactive mushrooms' (2009)
  3. [3]Dinis-Oliveira et al., 'Human and experimental toxicology of orellanine' (2016)

How we research this: sources, evidence grading, review and updates.