Since the beginning of mushroom season in Northern California last September, one person has required a liver transplant and three others have suffered life-threatening injuries after eating poisonous wild mushrooms that pop up in parks and gardens with the first rains.

Every year on average, six to eight people in Northern California are severely poisoned by mushrooms they collect, cook and eat. The threat is more serious than many people realize, said Dr. Kent Olson, medical director of the San Francisco Division of the California Poison Control System.

“It’s good news that the numbers are small,” Olson said. “But there’s a very high likelihood of death or liver injury that requires transplantation.”

In the Bay Area, mushroom-collecting season runs from September through May. Hundreds of fungus aficionados fan out into open spaces to find highly sought edible mushrooms such as chanterelles and king boletes.

Patients who suffer the most severe cases of mushroom poisoning require a liver transplant within a week in order to survive, Olson said.

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Of the four poisoning victims this mushroom season, two were family members. The other two cases were unrelated. Death cap mushrooms are suspected in all four cases, he said.

Death cap mushrooms, like this one on display at the recent Fungus Fair in Berkeley, are suspected in four poisonings since September (Gabriela Quirós)

With its non-descript appearance, the death cap doesn’t announce itself as a toxic mushroom, but together with its relative, the destroying angel mushroom, it is responsible for all of the life-threatening mushroom poisonings in California.

Also known by its scientific name Amanita phalloides, the death cap is whitish with green undertones and has a rounded cap. Across Northern California, it is often found under oak trees.

“In the Bay Area the numbers are exploding,” Olson said. “It has found a welcoming ecosystem to live in.”

The death cap’s poisonous relative, the destroying angel, or Amanita ocreata, is found mostly in the Los Angeles and Fresno areas.

Symptoms of death cap poisoning begin 8 to 12 hours after the mushrooms have been eaten, which delays treatment. Patients suffer from severe diarrhea, and as the toxins in the mushroom destroy their liver’s cells, their eyes and skin turn yellow and they become nauseous. If left untreated, victims can slip into a coma and die.

The death cap can be mistaken for an edible wild mushroom called coccora, to which it’s related, said J.R. Blair, former president of the Mycological Society of San Francisco, a non-profit group that organizes an educational fungus fair each December in the East Bay, as well as wild mushroom identification workshops.

The prized coccora mushroom is usually a golden-brown color, while the death cap is generally greenish. Coccora has furrows on the edge of its cap, as well as a layer of tissue on top of it, which the death cap lacks, Blair said.

“No one should be eating wild mushrooms without identification skills or without the affirmation of someone with sufficient knowledge,” said Blair. “There are no shortcuts.”

In the case of wild mushrooms, a little knowledge can be dangerous. Olson described the patient who required a liver transplant in November as someone “who frequently collected and ate wild mushrooms.” That has been true of many of the people who have poisoned themselves over the years, he said.

“Typically it is someone who has been mushroom picking before, who thinks they can tell the difference between dangerous and not,” he said.

Two of the people who were poisoned this season were members of a family who went out mushroom collecting in the Sierra foothills in October.

“Grandmother picked them, grandpa cooked them and they brought them home to family,” Olson said. Two family members suffered life-threatening symptoms, but survived without the need of a transplant. Another family member suffered minor symptoms.

The fourth victim this season was a homeless person who picked the mushrooms in Golden Gate Park in January, he said.

The Mycological Society of San Francisco and the Fungus Federation of Santa Cruz have experts who can help the public with the identification of mushrooms, said Blair.

Watch fungus expert J.R. Blair compare death cap and coccora mushrooms as part of this QUEST 6-minute video on the Fungus Fair in Berkeley last December.

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Life-Threatening Mushroom Poisoning