Following a mushroom bloom in the San Francisco Bay Area in late 2016,14 people consumed a poisonous fungus and fell drastically ill. One child even suffered permanent neurological damage. These were just some of the latest in a string of poisonings over the past few decades — a small handful of which proved to be fatal. The toxic cause: Amanita phalloides, better known by its grim moniker, the "death cap" mushroom.
Amanita phalloides is what's known in the world of mycology as a "mutualist," according to Anne Pringle, the Letters and Science Rubenstein Professor of Botany and Bacteriology at the University of Wisconsin-Madison. "A mutualism is, very simply, a relationship between two organisms of different species that result in a benefit for both organisms," says Pringle. As an ectomycorrhizal fungus (a fungus that grows outside the plant's roots), the death cap mushroom forms this relationship with a host tree. The fungus grows in the soil and mingles with the tree's roots, drawing out nitrogen from the soil and bringing it to the tree in exchange for carbon.
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In California, where the death cap mushroom is fairly common — possibly due to its pleasant Mediterranean climate — the fungus normally grows in tandem with coast live oak. On the east coast, the fungus usually attaches to pine. And in the fungus' native Europe, it's a combination of beech and oak.