The Paxillus involutus, commonly known as brown roll-rim, is a type of extremely poisonous fungi which fruits late summer- late winter. Due to its simple anatomy and brown colour, it can be confused with the penny bun mushroom, Boletus edulis, which has pores instead of gills. This, however, could potentially be a fatal mistake as the penny bun is edible whereas the brown roll-rim fungi is toxic. Additionally, it may be mistaken as a type of milk cap mushroom (Lactarius sp.), but as it doesn’t produce a milk-like substance from the gills it can quickly be distinguished.
Etymology:
The genus name Paxillus means ‘peg’ or ‘small stake’ whereas involutus means in-rolled. This is in reference to the cap margin that curves inwards, often seen in young fruit. This is also where the common name brown roll-rim came from.
Habitat:
This is a common fungus which is found throughout the UK, mainly spotted in woodlands with birch trees, heath/ grasslands and gardens and parks. They form ectomycorrhizal relationships with hardwoods and conifers so are often found near these trees. Furthermore, they often grow in groups.
Anatomy:
Caps and Flesh- The cap is a light brown to rusty brown colour, with pale brown/yellow flesh, between 5-12cm wide with a rolled margin. They are initially convex shaped which flattens out and becomes depressed in the centre as the fungi grows. It has a downy texture when young, which becomes smoother with age; and a viscid, slimy texture when wet.
Gills- The gills are a pale yellow colour which turns to dark brown when bruised. They are crowded and decurrent, running down the stem. Despite the obvious gills on this mushroom, it is actually a part of the order Boletales which are mushrooms with pores. This order forms the ectomycorrhizal relationships with trees.
Stem- The stem is 8-12 cm is diameter, and 6-12 cm long. It has a slight curve and is a light cream colour which fades to a darker brown with bruising and age.
Poisonous features:
This mushroom has no distinctive odour with a very acidic taste. This fungi is very fatal, and deadly to humans so consumption is extremely discouraged. It is known that Paxillus involutus is highly poisonous, however the exact toxin that causes this is unknown. The toxic component works by triggering the immune system to attack red blood cells (haemolytic anaemia), causing autoimmune damage which can lead to acute kidney shock and acute respiratory failure. While this mushroom does lose some toxicity once picked and boiling multiple times, if consumed (especially regularly) different toxins will build up in the body, entering the bloodstream and damaging the red blood cells. If eaten in small amounts, there may be no immediate reactions until months or even years later where the organism will suffer from a sudden, extreme allergic reaction or from haemolytic anaemia.
In 1944 the professional mycologist, Julius Schaeffer, died after eating this fungi, and is known to be the only mycologist to die of fungus poisoning. Since then, it is still consumed in areas of Eastern Europe and still causes deaths every year.
Reading list:
Latest posts:
Anabelle's UEA Ecology Blog 