Nature & living things

Eaten safely for decades, then it turns your blood against you

The brown roll-rim is a common brown mushroom with a funnel-shaped, inward-curling cap and gills that run down the stem, sometimes becoming pore-like near the base. First described in the 1780s, it was eventually given its own genus by Elias Magnus Fries, who recognized that despite its gills it belongs with the pored boletes rather than true agarics. Genetic studies have since complicated the picture further, suggesting what looks like one species is actually several closely related lineages that differ subtly in habitat and growth habit, some tied to conifers and others to birch and parkland trees, with at least one population possibly introduced from North America into European gardens.

Ecologically the fungus is a generalist, forming root partnerships with a wide range of trees and offering real benefits in return: it boosts seedlings' resistance to a common root-rot pathogen and reduces the uptake of toxic metals like cadmium and zinc by binding them in its own tissue. It also reshapes the bacterial communities living around tree roots, trading its own toxic waste products for growth-boosting acids the bacteria produce. Native across the Northern Hemisphere and especially fond of damp, non-chalky woodland and birch plantings, it has hitchhiked in the soil of imported European trees to Australia, New Zealand, South Africa and South America. It even thrives in polluted forests where more sensitive fungi decline, and its fruiting bodies can play host to flies, beetles and a parasitic mould that turns them a golden, powdery colour.

For decades the mushroom was eaten across Central and Eastern Europe, usually pickled or cooked, despite causing stomach upsets when eaten raw. That changed after a German mycologist died in 1944 following a meal of the fungus, which triggered kidney failure. Research later revealed the real danger: an unidentified antigen that, after repeated exposure, can provoke the immune system into attacking the eater's own red blood cells, sometimes after years of apparently harmless consumption. The resulting autoimmune hemolysis can escalate rapidly into kidney injury, shock, respiratory failure and fatal complications, and there is no antidote, only supportive care such as steroids, plasmapheresis or dialysis. Guidebooks were slow to catch up, with some recommending the mushroom as edible into the late 1990s, and people in parts of Poland, Russia and Ukraine still die from eating it today.

It has gills, but it is more closely related to the pore-bearing boletes than to ordinary gilled mushrooms — and genetic work hints it may not be one species at all.

Read the whole of Paxillus involutus on Wikipedia

The article comes from Wikipedia and is licensed under CC BY-SA 4.0. The introduction above is our own.