Paxillus involutus

Paxillus involutus

The brown roll-rim or common roll-rim (Paxillus involutus (Batsch) Fr., 1838) is a mushroom belonging to the Paxillaceae family.

Systematic –
Eukaryota domain,
Fungi Kingdom,
Division Basidiomycota,
Class Basidiomycetes,
Order Boletales,
Paxillaceae family,
Genus Paxillus,
Species P. involutus.
Basionym: Agaricus involutus Batsch 1786.
The terms are synonymous:
– Agaricus adscendibus Bolton;
– Agaricus contiguus Bull.;
– Agaricus involutus subsp. truncigenus Pers.;
– Agaricus involutus var. stillans Pers.;
– Agaricus involutus var. terrestris Alb. & Schwein.;
– Agaricus involutus var. truncigenus Alb. & Schwein.;
– Omphalia involuta (Batsch) Gray;
– Omphalia involuta subsp. truncigena (Pers.) Gray;
– Paxillus involutus f. eburneus Gelardi, Segneri & Vizzini;
– Paxillus involutus f. subrubicundulus Bon;
– Paxillus involutus var. excentricus Fr.;
– Paxillus involutus var. leptopus (Fr.) Quél.;
– Paxillus involutus var. simplex Peck;
– Paxillus involutus var. subinvolutus;
– Paxillus leptopus Fr.;
– Rhymovis involuta (Batsch) Rabenh.;
– Tapinia involuta (Batsch) Pat.;
– Tapinia involuta (Fr.) Berk..

Etymology –
The term Paxillus comes from the Latin paxillus, meaning “peg, stick,” referring to the mushroom’s general appearance or the more slender shape of some fruiting bodies in the genus.
The specific epithet involutus comes from the Latin involutus, meaning “rolled up, folded,” which indicates the strongly involuted cap margin in young specimens, a distinctive morphological characteristic.

Geographic Distribution and Habitat –
Paxillus involutus is a cosmopolitan species of the Northern Hemisphere, present in much of Europe, Asia, and North America.
In these areas, it is often found in broadleaf, coniferous, and mixed forests, particularly on acidic and moist soils, but can also be found in meadows, grassy areas within forests, and near tree stumps or decaying wood.
The species typically bears fruit from late summer to late autumn (June–November under favorable conditions), with harvest peaks especially in autumn.
P. involutus has also been inadvertently introduced to southern continents (Australia, New Zealand, South Africa, South America), most likely via soil associated with imported European plants.
It forms ectomycorrhizal relationships with a wide range of trees, including birch (Betula), pine (Pinus), oak (Quercus), beech (Fagus), and others, contributing to the exchange of nutrients between the soil and the host plant and improving the ability to withstand biotic and abiotic stress.

Recognition –
The morphology of Paxillus involutus is well-defined but can vary with age and environmental conditions.
The cap is 4–15 cm in diameter, initially convex, then flat, and finally slightly funnel-shaped.
The margin is long and involute, often grooved in the juvenile stages.
The surface varies from olive-brown to ochre-brown or tobacco, and becomes sticky when wet.
The gills are dense and decurrent on the stipe, light ochre in color, changing to rust-brown as the spores mature. They tend to anastomose and bifurcate, giving a reticulated appearance near the stipe.
The stipe measures 3–8 cm × 1–2 cm, cylindrical, often eccentric, and tapering toward the base. It is concolorous to the cap but may darken when handled.
The flesh is firm and juicy, yellow-ochre inside, and browns rapidly in the air with a faint, mushroomy/fruity odor; the flavor is slightly bitter or acidic.
Under the microscope, ellipsoidal ovoid spores measuring approximately 7–10 × 4.5–6 µm are observed, with a rusty-brown spore print.
The species can be confused with other lamellar fungi (e.g., some Lactarius or related species of the Paxillus genus), but the combination of a persistent involute margin, decurrent gills, and rapid browning when handled is diagnostic.

Cultivation –
Paxillus involutus is of no nutritional or commercial interest for cultivation, as it is a toxic and inedible species.
However, it is the subject of forestry studies related to mycorrhization: under experimental conditions, its association with host plants, such as Scots pine (Pinus sylvestris), can improve seedling tolerance to nutrient deficiencies (e.g., phosphorus) and biotic or abiotic stress conditions, thanks to its ability to mobilize nutrients in the soil and regulate the uptake of heavy metals.
These characteristics have made P. involutus useful as a model for studying ectomycorrhizal relationships in the laboratory, but not as a species cultivated for food.

Uses and Traditions –
In mycological and popular tradition, the species has numerous common names, including “paxillo involuto” and “agarico accartocciato” in Italian; “brown roll-rim” and “common roll-rim” in English. There are also several dialect names.
Historically, Paxillus involutus was considered edible after extensive cooking in some regions of Central and Eastern Europe and was consumed, for example, salted or pickled.
The belief in its edibility proved dangerous and faded with the accumulation of poisoning cases, some of which were serious or fatal.
The most famous case is that of the German mycologist Julius Schäffer, who died after consuming the species during World War II.
Today, the species is cited culturally more as an example of a mushroom “dangerous even after cooking” and a warning of the need for constant updating in mycological guides.

Preparation Methods –
Let’s be clear right away: there are no safe preparation methods to make Paxillus involutus edible.
Prolonged cooking, drying, or other traditional techniques do not eliminate the antigens responsible for hemolytic (paxillic) syndrome, which can cause serious immune reactions.
Paxillic syndrome is an immunohemolytic reaction: a species antigen stimulates the production of antibodies that subsequently attack red blood cells, potentially causing hemolytic anemia, acute kidney injury, shock, and multiple organ failure.
For these reasons, any form of consumption is strictly discouraged.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Cetto B., 2008. I funghi dal vero, Saturnia, Trento.
– Pignatti S., 1982. Flora d’Italia, Edagricole, Bologna.
– Conti F., Abbate G., Alessandrini A., Blasi C. (eds.), 2005. An annotated checklist of the Italian vascular flora, Palombi Editore.

Photo source:
– https://inaturalist-open-data.s3.amazonaws.com/photos/571566907/original.jpg
– https://upload.wikimedia.org/wikipedia/commons/8/83/L%27agaric_contigu_%28Paxillus_involutus%29.jpg

Warning: The pharmaceutical applications and dietary uses are provided for informational purposes only and do not in any way constitute medical prescriptions. We therefore decline any responsibility for their use for curative, aesthetic, or nutritional purposes.