Panzerotto (Paxillus involutus) – Ein Pilz, der im rohen Zustand giftig ist!

Morphological characteristics of the Brown Roll-Rim (Paxillus involutus)

Cap description

The cap of the Brown Roll-Rim has dimensions varying between 5 and 15 cm in diameter, although exceptional specimens can reach 20 cm. The shape is initially convex with a strongly inrolled margin (a characteristic from which the specific epithet "involutus" derives), then it gradually flattens out, becoming funnel-shaped in mature specimens. The cuticle is dry, velvety in young specimens, becoming smoother with age. The color varies from yellow-ochre to brownish-olive, often with darker tones in the center.

An important distinctive characteristic is the tendency of the margin to fade with age, assuming lighter tones compared to the rest of the cap. In humid conditions, the surface can become slightly sticky, but never truly hygrophanous as in other genera (e.g., Hygrophorus).

Gills and hymenophore

The hymenophore of the Brown Roll-Rim consists of dense gills, decurrent on the stem, easily separable from the cap flesh. The gills are dirty yellow or ochraceous in color in young specimens, becoming brown-rusty with spore maturation. A peculiar characteristic is the tendency of the gills to anastomose (join together) towards the stem, forming a sort of network.

To the touch, the gills are fragile and tend to darken considerably following pressure or rubbing. This browning is due to the oxidation of phenolic compounds contained in the mushroom and is considered an important diagnostic feature.

Stem and supporting structure

The stem of the Brown Roll-Rim is generally short and stout, measuring 3-8 cm in height and 1-2.5 cm in diameter. The shape is cylindrical or slightly clavate, often eccentric relative to the cap. The color is similar to that of the cap but tends towards lighter shades, especially in the upper part. The stem surface is smooth or finely fibrillose, without a ring or other remnant veil structures.

Internally, the stem is full and firm in young specimens, becoming hollow or spongy with aging. The base can sometimes appear slightly rooting, especially in specimens growing in compact soils.

Flesh and microscopic characteristics

The flesh of the Brown Roll-Rim is compact but soft, pale yellow in color. It tends to brown rapidly upon exposure to air following cutting or damage, a characteristic due to the enzyme laccase oxidizing phenolic compounds. The odor is weak, fungal, sometimes described as sour or fruity, while the taste is tending to be acrid or slightly bitter.

Microscopic analysis reveals smooth, elliptical spores, measuring 7-10 × 4.5-6 μm, brown in mass. The basidia are clavate and tetrasporic, while the hyphae present clamp connections, a common characteristic in most basidiomycetes.

Habitat and distribution of the Brown Roll-Rim

Geographical and seasonal distribution

Paxillus involutus is a cosmopolitan species widely distributed throughout Europe, North America, and northern Asia. In Italy, it is common in all regions, from the Alps to Sicily, although it is more frequent in the central-northern areas. Its fruiting season ranges from late spring to late autumn, with production peaks during rainy periods between August and October.

Ecology and mycorrhizal symbiosis

The Brown Roll-Rim is an obligately mycorrhizal fungus, forming symbiotic associations with numerous tree species. Its ecological preferences are broad, demonstrating notable plasticity in adapting to different environmental conditions. It prefers acidic or neutral soils, moist but well-drained, and is often associated with path edges, clearings, and disturbed areas.

Among the tree species with which it most frequently establishes mycorrhizal relationships are:

• Birch (Betula pendula, Betula pubescens)
• Poplar (Populus spp.)
• Willow (Salix spp.)
• Alder (Alnus spp.)
• Beech (Fagus sylvatica)
• Oak (Quercus spp.)
• Pine (Pinus spp.)
• Spruce (Picea abies)

This wide range of host plants contributes to the vast distribution of the fungus and its ability to colonize different environments. The mycorrhizal symbiosis of Paxillus involutus is of the ectomycorrhizal type, with the formation of a hyphal mantle around the fine roots of the host and the development of hyphae that penetrate the intercellular spaces of the root cortex.

Toxicity of the Brown Roll-Rim: mechanisms and hemolytic syndrome

Toxic principles and their characteristics

The Brown Roll-Rim contains several toxic principles, among which the most important are:

1. Involutin: a compound responsible for the characteristic browning of the flesh and gills. Although not highly toxic by itself, it can contribute to sensitization reactions.
2. Lectins: proteins capable of specifically binding to carbohydrates on the cell surface, causing agglutination of red blood cells.
3. Protein antigens: capable of triggering immune reactions in sensitized subjects.

The main toxin responsible for the hemolytic syndrome is a heat-labile antigen that stimulates the production of IgG antibodies. These antibodies, following subsequent ingestion of the mushroom, form immune complexes that deposit on the surface of erythrocytes, activating the complement system and causing hemolysis (destruction of red blood cells).

Paxillus hemolytic syndrome: immunological mechanism

The hemolytic syndrome from Brown Roll-Rim is a reaction of the type II (cytotoxic) immunological type. The mechanism involves several phases:

1. First exposure (sensitization): ingestion of the mushroom, even in small quantities, induces the production of specific IgG antibodies against antigens present in Paxillus involutus.
2. Second exposure (immune reaction): subsequent consumption of the mushroom, even months or years later, determines the formation of antigen-antibody complexes that bind to the surface of erythrocytes.
3. Complement activation: the immune complexes activate the complement cascade, leading to the formation of the membrane attack complex (MAC) that perforates the erythrocyte membrane.
4. Intravascular hemolysis: the destruction of red blood cells releases hemoglobin into the plasma, resulting in hemolytic anemia, jaundice, and possible acute renal failure.

This mechanism explains why some consumers may eat the mushroom for years without apparent consequences, only to develop a severe reaction even after ingestion of modest amounts.

Risk factors and individual variability

The reaction to the Brown Roll-Rim shows notable individual variability, influenced by several factors:

• Frequency of consumption: habitual consumers have a higher probability of developing sensitization.
• Quantity ingested: although the reaction is not strictly dose-dependent, larger quantities increase the risk.
• Preparation method: cooking reduces but does not completely eliminate the responsible antigens.
• Genetic factors: some individuals might be genetically predisposed to develop more intense immune responses.
• Health status: immunosuppression conditions or autoimmune diseases can modify the response.

History of toxicological classification

From folk tradition to scientific awareness

For centuries, the Brown Roll-Rim was consumed in various European regions, especially in Eastern Europe and some areas of Italy. Folk traditions recommended prolonged cooking (often double boiling with water change) to eliminate the acrid taste and the presumed "poison". In some regions, it was also preserved in pickle after adequate pre-cooking.

The first suspicions about its toxicity emerged in the first half of the twentieth century, with sporadic reports of adverse reactions. However, these cases were often attributed to individual intolerances or identification errors, without a systematic investigation into the causes.

The german case of 1944 and subsequent confirmations

The turning point in understanding the toxicity of the Brown Roll-Rim occurred in 1944, when the German mycologist Julius Schäffer described for the first time the hemolytic syndrome in a habitual consumer. Schäffer observed that the patient, who had consumed the mushroom regularly for years, developed a severe hemolytic reaction after a meal apparently identical to previous ones.

In the following years, numerous similar cases were documented throughout Europe, allowing the complete clinical picture of the hemolytic syndrome from Paxillus to be outlined. Particularly significant was the work of the Italian toxicologist Giovanni Negri, who in the 1960s helped clarify the immunological mechanisms underlying the reaction.

The official reclassification

The progressive accumulation of scientific evidence led, starting in the 1970s, to an official reclassification of Paxillus involutus as a toxic species. The main European mycological societies, including the Associazione Micologica Bresadola in Italy, began to categorically advise against its consumption, regardless of the preparation methods.

Today, the Brown Roll-Rim is included in the toxic species lists of all major mycological publications, and its consumption is expressly discouraged by the health authorities of numerous countries.

Confusion with similar species

Similar edible species

Among the edible species with which the Brown Roll-Rim can be confused, the main ones are:

• Lactarius deliciosus (Saffron Milk Cap): distinguished by the emission of orange latex upon breaking and by the non-anastomosing gills.
• Cantharellus cibarius (Chanterelle): presents false gills (folds) instead of true gills, and does not bruise upon handling.
• Craterellus cornucopioides (Horn of Plenty): has a smooth or barely veined hymenophore, a more pronounced funnel-shaped cap, and a blackish color.

Other similar toxic species

The Brown Roll-Rim can also be confused with other toxic species, including:

• Paxillus filamentosus: a similar species but with a more fibrillose cap and generally smaller dimensions.
• Omphalotus olearius (Jack-o'-lantern mushroom): a bioluminescent fungus, with decurrent yellow-orange gills and cespitose growth on wood.
• Tapinella atrotomentosa: grows on conifer wood, has an eccentric or lateral stem, and a blackish velvety surface.

Toxicological insights and recent research

Studies on molecular mechanisms of toxicity

Recent research has focused on the identification and characterization of the specific lectins present in Paxillus involutus. These proteins, named involutins, show specificity for certain carbohydrates present on the surface of erythrocytes and other cells. Structural studies have revealed that these lectins possess particular binding sites that explain their selectivity.

Other studies have investigated the role of the complement system in the pathogenesis of the hemolytic syndrome. It has been demonstrated that the antigen-antibody complexes formed after ingestion of the mushroom preferentially activate the classical complement pathway, leading to the formation of the membrane attack complex (MAC) on erythrocytes.

Research on potential applications

Despite its toxicity, the Brown Roll-Rim is attracting research interest for possible biotechnological applications. In particular:

• Ligninolytic enzymes: Paxillus involutus produces enzymes capable of degrading lignin, with potential applications in industrial biotechnology and bioremediation.
• Detoxification systems: this fungus possesses efficient mechanisms for neutralizing heavy metals and other pollutants, thanks to the production of metallothioneins and other chelators.
• Bioactive compounds: some secondary metabolites isolated from the Brown Roll-Rim show antimicrobial and antitumor activity in preliminary in vitro studies.

Ecological research and climate change

The Brown Roll-Rim is also the subject of ecological studies, particularly regarding its response to climate change and pollution. Research conducted in different European regions has highlighted that this species shows notable resilience to environmental alterations, maintaining its mycorrhizal associations even under stress conditions.

Other studies have focused on the ability of Paxillus involutus to accumulate radionuclides, particularly cesium-137, making it a potential bioindicator of radioactive contamination in forest ecosystems.

Recommendations for foragers

Guidelines for safe identification

To avoid confusing the Brown Roll-Rim with edible species, foragers should:

1. Carefully observe the cap margin: the characteristic inrolling is an important diagnostic element.
2. Verify the behavior of the gills under pressure: immediate browning is a warning signal.
3. Check the ease of separation of the gills: in the Brown Roll-Rim, they detach easily from the flesh.
4. Pay attention to the habitat: growth in groups in mixed woods is typical.

Recommendations for safe consumption

Considering the confirmed toxicity of the Brown Roll-Rim, the only safe recommendation is:

In case of doubts about the identification of a mushroom, it is always advisable to:

• Consult an expert mycologist or a local mycological inspection office for verification.
• Consult updated mycological guides that report the toxicity of the Brown Roll-Rim.
• Participate in mycology courses to improve your identification skills.

Brown Roll-Rim: a mushroom not to be consumed!

The toxicity of the Brown Roll-Rim, linked to complex and unpredictable immunological mechanisms, categorically advises against its consumption in any form. The hemolytic syndrome it can trigger represents a serious health risk, with possible fatal outcomes in the absence of timely treatment.

For mycologists, mycophiles, and all mushroom enthusiasts, the case of the Brown Roll-Rim underscores the importance of:

• Staying updated on the latest discoveries in the field of mycotoxicology.
• Deepening knowledge about the morphological characteristics of species.
• Practicing responsible and conscious foraging.
• Being wary of folk traditions not verified scientifically.

Mycology, like all sciences, is in continuous evolution, and the case of the Brown Roll-Rim remains an important warning about the importance of the scientific approach in the study and consumption of mushrooms.