Paxillus involutus

Description

Paxillus involutus is a poisonous mushroom found worldwide, often introduced accidentally through soil attached to European trees. It features a distinctive appearance with various shades of brown, a funnel-shaped cap, and gills that can appear pore-like near the stem. Despite having gills, it's more closely related to pored boletes than typical gilled mushrooms. The mushroom's toxicity varies by region, with reports of it being considered edible in the western United States but decidedly toxic in Europe, and symptoms of poisoning include vomiting, diarrhea, abdominal pain, and decreased blood volume.

Intriguingly, a Swiss physician in the 1980s discovered an antigen in Paxillus involutus that triggers an autoimmune reaction, causing the body's immune cells to attack its own red blood cells. Despite this discovery, clear warnings against consuming these mushrooms did not emerge until 1990, and there were even instances where they were recommended as edible. In Germany, intoxications from this mushroom, even when cooked well, have increased over time, and there is no known antidote for poisoning, with treatment relying on supportive care and monitoring various health parameters.

Additionally, Paxillus involutus contains substances that can damage chromosomes, although it's uncertain whether these have carcinogenic or mutagenic properties. It's important to exercise caution with all Paxillus species, as they are universally considered toxic and not safe for consumption.

The most important feature is the browning of the flesh/gills when pressure is applied!

Common names: Poison Paxillus, Brown Roll-rim, Common Roll-rim, Japan (ヒダハタケ), German (Kahler Krempling).

Mushroom Identification

1. Cap

   1.57 to 5.91 inches (4 to 15 cm) wide, initially curved with a fuzzy edge, later becoming flat or slightly depressed. It can be sticky or dry and comes in shades of brown, yellow-brown, olive brown, or grayish brown.

2. Gills

   These are close together, often turning wrinkled or pore-like near the stem. They are typically yellowish to pale cinnamon or pale olive and can turn brown when bruised.

3. Stem

   Usually 0.79 to 3.15 inches (2 to 8 cm) long and up to 0.79 inches (2 cm) thick, tapering towards the base. It's dry, smooth, or finely hairy, and its color matches the cap or is lighter. The stem can also bruise brownish to reddish brown.

4. Flesh

   The flesh is thick and firm, appearing yellowish but turning brown when exposed.

5. Odor and Taste

   It has an acidic or nondescript taste and a somewhat faint or indistinct odor.

6. Chemical Reactions

   Applying KOH to the cap surface results in a gray color change.

7. Spore Print

   The spore print is purplish brown to yellow-brown.

8. Habitat

   It is typically found in North America and Europe in woodlands and urban areas during the summer and fall. It forms mycorrhizal relationships with various hardwood and conifer trees and can also live as a saprobe on decaying wood.

9. Microscopic Features

   Spores are smooth, elliptical, measuring 6.5-10 x 5-7 µ. Pleuro- and cheilocystidia are somewhat fusoid and 40-90 µ long with brown contents. The pileipellis is a cutis with elements 3-6 µ wide and brownish contents. Clamp connections are present.

Look-Alikes

1. Tapinella atrotomentosa

   Larger mushroom with a velvety cap and a short, thick stem covered in dark brown fuzz. Typically found on or near conifer tree stumps.

2. Paxillus rubicundulus

   Similar in appearance but has smaller spores (5.5-8.5 x 4-5μm). Forms mycorrhizal relationships with Alder trees.

3. Lactarius turpis

   Resembles Paxillus involutus but with a darker olive coloration.

4. Paxillus vernalis

   Found in North America, it has a darker spore print, a thicker stem, and is associated with aspen trees.

5. Paxillus filamentosus

   A close relative with similar appearance to Paxillus involutus, but it can be distinguished by pressed-down scales on the cap surface, light yellow flesh that bruises only slightly brown, and deep yellow-ochre gills that don't change color upon injury.

6. Paxillus obscurisporus

   Larger than Paxillus involutus with caps up to 40 cm wide, and cream-colored mycelia covering the stipe's base. Caps tend to unroll and flatten with age.

7. Paxillus validus

   Found only in Europe, it has caps up to 20 cm wide and a stipe of nearly uniform width. It can be distinguished by the presence of longer crystals in the rhizomorphs.

History

In 1785, French mycologist Jean Baptiste Francois Bulliard described a toxic toadstool and called it Agaricus contiguus. However, in 1786, August Batsch described it as Agaricus involutus, which is now considered the first proper description of the Brown Rollrim mushroom.

Later on, the renowned Swedish naturalist Elias Magnus Fries created the genus Paxillus, with Paxillus involutus as the main representative. Another French mycologist, René Maire, placed the Paxillus genus into a new mycological family known as Paxillaceae. More recently, the Paxillus genus was revised using mating studies and DNA analysis. This resulted in some species, like Paxillus atrotomentosus, being reclassified as Tapinella atrotomentosa because they grow on wood instead of as mycorrhizal soil-based fungi.

The current scientific name used in the Kew Gardens and British Mycological Society checklists dates back to Christiaan Hendrik Persoon's 1801 publication. The name Paxillus comes from the Latin word for "peg" or "small stake," and the specific epithet involutus refers to the rolled-in margin of young fruitbodies.

Synonyms

• Agaricus lateralis Schaeffer (1774), Fungorum qui in Bavaria et Palatinatu circa Ratisbonam, 4, p. 31, tab. 71-72

• Agaricus contiguus Bulliard (1784), Herbier de la France, 5, tab. 240 & tab. 576, fig. 1

• Agaricus involutus Batsch (1786), Elenchus fungorum, continuatio prima, p. 39, tab. 13, fig. 61 (Basionyme) Sanctionnement : Fries (1821)

• Agaricus adscendens Bolton (1788), An history of fungusses growing about Halifax, 2, p. 55, tab. 55 ('adscendibus')

• Agaricus adustus Withering (1792), A botanical arrangement of British plants, Edn 2, 3, p. 301

• Hypophyllum scyphus Paulet (1808) [1793], Traité des champignons, 2, p. 157, tab. 62

• Hypophyllum infundibuliforme Paulet (1808) [1793], Traité des champignons, 2, p. 157, tab. 63, fig. 1

• Hypophyllum fossarum Paulet (1808) [1793], Traité des champignons, 2, p. 156, tab. 61, fig. 1-2

• Omphalia involuta (Batsch) Gray (1821), A natural arrangement of British plants, 1, p. 611

• Ruthea involuta (Batsch) Opatowski (1836), Archiv für naturgeschichte, 2(1), p. 4

• Rhymovis involuta (Batsch) Rabenhorst (1844), Deutschlands kryptogamen-flora, 1, p. 453

• Tapinia involuta (Batsch) Patouillard (1887), Les hyménomycètes d'Europe, anatomie générale et classification des champignons supérieurs, p. 130

• Paxillus lateralis (Schaeffer) Saccardo (1916), Flora italica cryptogama. Pars 1: Fungi. Hymeniales, 1(15), p. 669

Video

Photo copyright:

All photos were taken by the Ultimate Mushroom team and can be used for your own purposes under the Attribution-ShareAlike 4.0 International license.