Deadly Webcap

Cortinarius rubellus is native to the temperate and boreal forests of Europe and has also been documented in parts of North America, though its exact distribution remains under study due to taxonomic confusion with closely related species.

• First described by the Swedish mycologist Elias Magnus Fries in the 19th century
• The genus Cortinarius is one of the most species-rich genera of macrofungi, with estimates ranging from 2,000 to over 3,000 species globally
• Molecular phylogenetic studies have revealed that many Cortinarius species previously identified by morphology alone actually represent complexes of cryptic species
• C. rubellus is part of the subgenus Orellani, which contains several species producing the lethal toxin orellanine
• Its range extends from Scandinavia through Central Europe to the British Isles, and it has been reported in coniferous and mixed forests across these regions

The Deadly Webcap is a medium-sized agaric mushroom with distinctive but subtle features that make it dangerously easy to misidentify.

Cap:
• 3–10 cm in diameter, initially convex to bell-shaped, becoming broadly convex to flat with age
• Surface is dry, smooth to slightly fibrillose, with a reddish-brown to tawny-orange color
• Margin is often slightly striate (grooved) when moist
• Flesh is pale yellowish-brown, with no distinctive odor or a faintly radish-like smell

Gills:
• Adnate to slightly decurrent, moderately crowded
• Color progresses from pale ochre in youth to rusty brown as spores mature
• A cobweb-like partial veil (cortina) covers the gills in young specimens, leaving faint remnants on the stipe

Stipe (Stem):
• 5–12 cm tall, 0.5–1.5 cm thick, roughly equal or slightly swollen at the base
• Color is pale yellowish to tan, sometimes with faint reddish-brown fibrils
• Remnants of the cortina may form faint ring zones on the upper stipe
• Base is often slightly bulbous, sometimes with a faint volval margin

Spores:
• Spore print is rusty brown to cinnamon-brown
• Spores are ellipsoid to almond-shaped, 8–11 × 5–7 µm, with a finely warty (verrucose) surface
• Basidia are 4-spored, clavate, approximately 25–35 × 7–10 µm

Cortinarius rubellus is an ectomycorrhizal fungus, forming obligate symbiotic relationships with the roots of certain trees. This ecological role is essential for nutrient exchange in forest ecosystems.

• Forms ectomycorrhizal associations primarily with conifers, especially spruce (Picea) and pine (Pinus), and occasionally with birch (Betula)
• Found in acidic, nutrient-poor soils in coniferous and mixed forests
• Fruits in late summer to autumn (typically August to November in the Northern Hemisphere)
• Often grows in mossy areas, particularly among sphagnum moss and under dense conifer canopies
• The mycelium extends the root surface area of host trees, facilitating uptake of phosphorus, nitrogen, and water in exchange for photosynthetically derived carbon
• Fruiting bodies appear solitarily, scattered, or in small groups
• Prefers cool, moist conditions and is most commonly encountered after heavy rainfall

The Deadly Webcap is one of the most dangerously poisonous mushrooms in the world, containing the nephrotoxic compound orellanine.

• Primary toxin: orellanine (3,3',4,4'-tetrahydroxy-2,2'-bipyridine-1,1'-dioxide), a bipyridine N-oxide compound structurally related to the herbicides paraquat and diquat
• Orellanine causes severe, often irreversible damage to the renal tubules, leading to acute kidney failure
• The lethal dose in humans is estimated at approximately 10–20 mg of orellanine, which can be present in as few as 1–2 mushrooms
• Symptoms are notoriously delayed, typically appearing 2–14 days after ingestion (average 6–8 days), which often leads to delayed diagnosis and treatment
• Initial symptoms include nausea, vomiting, abdominal pain, headache, and chills, mimicking a common gastrointestinal illness
• This is followed by intense thirst, frequent urination, and then a dangerous reduction in urine output (oliguria or anuria) as kidney function deteriorates
• There is no specific antidote; treatment is supportive and may require hemodialysis or kidney transplantation
• Several fatalities have been documented in Europe, particularly in Poland, Scandinavia, and the British Isles, often due to confusion with edible chanterelles or other harmless brown mushrooms
• Cooking, drying, and freezing do not destroy orellanine — the toxin is heat-stable and water-soluble
• The related species Cortinarius orellanus and Cortinarius splendens also contain orellanine and pose similar dangers

Cortinarius rubellus is NOT cultivated and should NEVER be intentionally grown, handled for consumption, or ingested under any circumstances. It is an extremely dangerous poisonous fungus.

• This species cannot be reliably distinguished from edible look-alikes without microscopic examination and molecular analysis
• Even experienced mycologists exercise extreme caution when identifying Cortinarius species in the subgenus Orellani
• Foraging for wild mushrooms without expert guidance carries significant risk, particularly for brown agarics in the genus Cortinarius
• If accidental ingestion is suspected, seek immediate medical attention and bring a specimen of the mushroom for identification
• The delayed onset of symptoms means that patients may not connect their illness to a mushroom meal consumed days or weeks earlier — always inform healthcare providers of any recent wild mushroom consumption