Everything about Paxillus Involutus totally explained
Paxillus involutus, commonly known as the
common- or
brown roll-rim, or
poison pax, is a
poisonous
basidiomycete fungus, previously considered edible and eaten widely in
Eastern and
Central Europe. It had been recognized as causing gastric upsets when eaten raw, but was more recently implicated in a potentially fatal immune
hemolysis in those who had consumed the mushroom without ill-effects for years. It often grows near edible mushrooms as well which makes it harder to identify by amateur mushroomers.
It is widely distributed across the
Northern Hemisphere and has been accidentally introduced to
Australia,
New Zealand, and
South America; it's likely to have been transported in soil of European trees to those countries. Various shades of brown in color, the fruiting body resembles a brown wooden top and may be found in deciduous and coniferous woods, and grassy areas in later summer and autumn. The cap bears a distinctive inrolled rim and decurrent gills which may be pore-like close to the stipe. Though gilled, it's more closely related to the pored
boletes than to typical gilled mushrooms.
Taxonomy
The brown roll-rim was described by French mycologist
Pierre Bulliard in 1785 as
Agricus contiquus, though the 1786 combination
Agaricus involutus of
August Batsch is taken as the first valid description. The Swedish mycologist
Elias Magnus Fries then erected the genus
Paxillus in 1838 and it gained its current
binomial name. The generic name is derived from the
Latin for 'peg' or 'plug' and the specific epithet
involutus meaning 'inrolled' refers to the inrolled cap.
Although it has gills rather than pores, it's has long been recognized as belonging to the pored mushrooms of the
Boletales; More recent molecular research confirms its relations; the genus
Gyrodon, with the decurrent-pored mushroom
G. lividus, is the closest group to the genus
Paxillus and together they lie near the base of a tree from which the genus
Boletus arises.
Description
Resembling a brown wooden
top, the
epigeous (aboveground)
fruiting body (basidiocarp) may be up to 6 cm (2½ in) high. The
spore print is brown, while the dimensions of the ellipsoid (oval-shaped) spores are 8 x 5 μm. Of similar color to the cap, the short
stipe can be crooked and tapers toward the base.
Its brownish color and funnel-like shape could lead to its confusion with several species of
Lactarius, though many of these have some degree of toxicity themselves.
Distribution and habitat
The brown roll-rim is found across the Northern Hemisphere, across Europe and Asia, with records from
Japan, and eastern
Anatolia in Turkey. It is widely distributed across northern North America. It can be found growing on
lawns and old
meadows throughout its distribution. Fruiting bodies are generally terrestrial, though may be found on woody material around tree stumps. and it has subsequently been recorded in
New South Wales,
Victoria, and
Western Australia. It has been recorded under introduced
birch (
Betula) and
hazel (
Corylus) in New Zealand. Singer reported a similar situation in South America, with the species recorded under introduced trees in Chile. It is likely to have been transported in soil of European trees to those countries.
Toxicity
Paxillus involutus was previously widely eaten in
Central- and
Eastern Europe, though English guidebooks didn't recommend it. It was known to be a gastrointestinal irritant when ingested raw but had been presumed edible after cooking. Questions were first raised about its toxicity after an German mycologist, Dr Julius Schäffer, died after eating it in October 1944. About an hour after he and his wife ate a meal prepared with the mushrooms, Schäffer developed vomiting, diarrhea, and fever. His condition worsened to the point where he was admitted to hospital the following day, and subsequently developed renal failure, perishing after 17 days. Flammer in 1980 discovered an
antigen within the mushroom which stimulates an
autoimmune reaction causing the body's immune cells to consider its own
red blood cells as foreign and attack them.
This relatively rare immunohemolytic syndrome occurs following the repeated ingestion of
Paxillus mushrooms. Most commonly it arises when the person has ingested the mushroom for a long period of time, sometimes for many years, and has shown mild
gastrointestinal symptoms on previous occasions. These complications can cause significant morbidity with fatalities having been reported.
There is no antidote for poisoning, treatment consists of monitoring
complete blood count, renal function, blood pressure, and fluid and electrolyte balance and correcting any abnormalities. The use of
corticosteroids may be a useful adjunct in treatment; corticosteroids protect blood cells against hemolysis thereby reducing complications. Plasmapheresis may also be beneficial in improving outcome. Plasmapheresis reduces the circulating immune complexes in the blood which cause the hemolysis, removing these complexes with
extracorporeal techniques such as plasmaphoresis can then reduce the immune hemolysis. Additionally
hemodialysis can be used as a supportive treatment for patients with compromised renal function or renal failure.
Further Information
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