Identify Brown Rollrim (Paxillus involutus) - Plant AI mycology guides
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Brown Rollrim

Scientific Name: Paxillus involutus

The Brown Rollrim, or Common Rollrim, is a highly common, deceptive, and lethally poisonous wild fungus native to woodlands and grassy parks across Europe, North America, and Asia. Growing in mycorrhizal symbiosis with Birch and Pine, it is a very common park mushroom. It features a yellowish-brown cap with a strongly, distinctly inrolled edge that is covered in fine, velvety hairs. Long considered a safe edible mushroom in Eastern Europe, modern science has revealed a terrifying, unique toxicity: it triggers a fatal autoimmune reaction known as Paxillus Syndrome.

🌍 Environment Birch & Pine Woodlands
💧 Humidity Moderate Humidity (65-75%)
🪵 Substrate / Host Damp Acidic Soil / Birch Roots
📏 Size 5cm - 12cm
🍄 Category Highly Toxic 💀
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How to Identify

A yellowish-brown cap with a strongly inrolled velvety margin and brownish-yellow gills that stain dark brown when touched.

  • Inrolled Velvety Margin: The cap margin is strongly and distinctly rolled inward toward the gills, remaining rolled in even when mature, covered in fine velvety hairs.
  • Brown-Bruising Gills: The gills are decurrent (running down the stem), pale brownish-yellow, and stain a dark, dingy brown instantly when touched.
  • Funnel-shaped Cap: A convex cap, 5 to 12 cm, that quickly becomes depressed in the center, forming a shallow brown funnel.
💀 Paxillus Syndrome: A terrifying immunological time bomb! Repeatedly eating this mushroom causes your body to produce antibodies against it. Eventually, these antibodies trigger a massive, fatal autoimmune reaction where your immune system attacks and destroys your own red blood cells (acute hemolysis), leading to kidney failure and death!

Detailed Mycology Profile & Safety Guide

Click on any dimension to expand detailed field guides, substrate requirements, and safety warnings.

Forms mycorrhizal relationships with Birch, Beech, and Pine. Fruits in large groups or lines on damp, acidic soils in woodlands, grassy parks, and garden borders from summer to late autumn.
Requires cool, damp autumn climates (8-16°C). It thrives in wet grass around municipal birch trees after autumn storms.
Tolerates open parks, but thrives best in partial shade under birch tree branches where soil moisture is high.
Cap is 5 to 12 cm, yellowish-brown to olive-brown, slimy when wet. Gills are decurrent, narrow, crowded, yellow-brown, bruising dark brown.
Produces a distinct rust-brown to yellowish-brown spore print. Spores are smooth and elliptical.
Flesh is thick, soft, yellowish, turning brown when cut, with a mild, slightly sour taste. Stem is short, thick, brownish, lacking a ring.
NEVER harvest. Discard any historical cookbooks that list it as edible. Warn others of its unique autoimmune toxicity. It is highly dangerous due to its delayed reaction.
Lethally poisonous. Eating it raw causes immediate gastrointestinal poisoning. Eating it cooked may cause no symptoms for years, until a sudden, lethal autoimmune hemolytic shock occurs after a random meal.
Contains **involutin** and other compounds that stimulate a unique antigen-antibody complex in human blood, triggering IgG-mediated red blood cell destruction.
CRITICAL WARNING: Deceptive look-alikes! The Brown Rollrim can be confused by East European foragers with the edible **Milk Caps** (Lactarius species) or **Brown Birch Bolete**. However, edible Milk Caps **exude a milky white or colored sap when the gills are cut**, which the Brown Rollrim **completely lacks**. Birch Boletes **have sponge-like pores instead of decurrent gills**. Always check for the inrolled velvety cap margin and decurrent, brown-bruising gills!
Paxillus involutus was widely eaten in Europe until the famous German mycologist Julius Schäffer died of kidney failure in 1944 after eating it. This led to the discovery of Paxillus Syndrome, proving that a mushroom can be eaten safely for years before suddenly triggering a fatal allergic-like autoimmune collapse.
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Margin Unrolling (Extreme Age)

Symptoms: The cap margin becomes flat or slightly wavy, losing its distinct rolled-in look.

Action: Action: This is caused by extreme maturity. The cap expands fully to release the last spores. The toxic compounds remain highly active; do not handle.

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Gill Mold

Symptoms: The decurrent brownish gills develop a white or yellow powdery mold coating in wet grass.

Action: Action: Discard. The crowded gills easily trap grass moisture, leading to mold decay. Avoid lawn compost contamination.

Frequently Asked Questions

Why is the Brown Rollrim considered so dangerous?

It is dangerous because of 'Paxillus Syndrome.' It is a cumulative poison. A person can eat it safely for years with zero symptoms, but their body is slowly building up antibodies. Suddenly, after a random meal, these antibodies trigger a massive autoimmune attack, destroying their own red blood cells.

What are the symptoms of Paxillus Syndrome?

The autoimmune reaction triggers sudden, violent hemolytic shock with kidney pain, dark urine (hemoglobinuria), severe jaundice, kidney failure, and death if immediate blood transfusion and dialysis are not received.

Does cooking destroy the toxins in this mushroom?

No. While cooking destroys the compounds that cause immediate stomach irritation, it has absolutely no effect on the antigens that trigger the fatal autoimmune Paxillus Syndrome.

How do you distinguish it from a Milk Cap?

Edible Milk Caps (Lactarius species) always exude a sticky, milky sap (latex) from their gills when scratched or cut. The toxic Brown Rollrim never exudes any milky sap, and its gills bruise a dark, dingy brown color.

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