Wet Weather Promotes Mushroom Growth, But Be Warned Some Are Deadly

FREMONT, CA — Mushrooms are plentiful this year thanks to abundant rains and visitors to any number of Fremont's city parks and nearby regional parks, including Coyote Hills Regional Park, Quarry Lakes Regional Recreation Area and Mission Peak Regional Preserve, have likely noticed them popping up in great numbers.

While mushrooms are an ecologically important part of parklands and can look beautiful, some contain dangerous toxins, one East Bay Regional Parks District representative said.

The death cap (Amanita phalloides) and western destroying angel (Amanita ocreata) are two of the world’s most toxic mushrooms, and both can be found in East Bay Regional Parks during the rainy season, the parks district said.

"The death cap and western destroying angel mushrooms contain amatoxins, molecules that are deadly to many animals," Jen Vanya, a public information specialist with East Bay Regional Park District, wrote in an email to Patch.com. "Symptoms may not appear until up to 12 hours after consumption, beginning as severe gastrointestinal distress and progressing to liver and kidney failure if treatment is not sought immediately."

East Bay Regional Park District Naturalist Trent Pearce documents and teaches about fungi in the Bay Area.

“Both of these mushrooms can be lethal to humans and pets if consumed,” Pearce warned. “They are mainly associated with oak trees and can be found growing anywhere oak roots are present.”

According to Vanya, the death cap is a medium to large mushroom that typically has a greenish-gray cap, white gills, a white ring around the stem, and a large white sac at the base of the stem. Although the death cap is mainly associated with oak trees, it has been found growing with other hardwoods. It was accidentally introduced to North America on the roots of European cork oaks and is now slowly colonizing the west coast. The death cap is not native to California.

The western destroying angel is a medium to large mushroom that usually has a creamy white cap, white gills, a white ring around the stem that can disappear with age, and a thin white sac at the base. It fruits from late winter into spring. It is associated exclusively with oaks. Unlike the death cap, it is a native California mushroom.

“The Park District urges the public to be safe and knowledgeable about toxic mushrooms when encountering them in the parks,” Vanya said. “Collecting any mushrooms in East Bay Regional Parks is not allowed.”

According to Vanya, the death cap and western destroying angel can also be dangerous for pets.

"Pet owners should contact a veterinarian immediately if they suspect their pet may have eaten a toxic mushroom,” she said.

While the death cap and western destroying angel mushrooms are responsible for most cases of mushroom poisonings in California, deadly toxins can also be found in Galerina and Lepiota mushroom species, which also occur in the Bay Area.

For more information about toxic mushrooms, visit East Bay Regional Parks Toxic Mushrooms website here.