Paxillus involutus, the common roll-rim, is a fungus that is widely distributed across the Northern Hemisphere and has also been unintentionally introduced to Australia, New Zealand, and South America. The brownish fruit body grows up to 6 centimetres (2.4 in) high. It has a funnel-shaped cap up to 12 centimetres (5 in) wide, with a distinctive in-rolled rim and decurrent gills close to the stalk. Genetic testing suggests that the fungus may be a species complex rather than a single species. A common mushroom of deciduous and coniferous woods and grassy areas in late summer and autumn, P. involutus is symbiotic with the roots of many tree species, reducing the trees' intake of heavy metals and increasing their resistance to pathogens. Previously considered to be edible and eaten widely in Eastern and Central Europe, the mushroom has been found to be dangerously poisonous; the German mycologist Julius Schäffer died from ingesting it in 1944. It can trigger the immune system to attack red blood cells with potentially fatal complications, including acute renal and respiratory failure. This P. involutus mushroom was photograhed on Golovec, a hill near Ljubljana, Slovenia.

Photograph credit: Petar Milošević