After the first fall rains, the East Bay hills come alive with mushrooms. Sprouting in an array of dazzling colors, these fungal fruitbodies can be beautiful – but some of them contain dangerous toxins.
The Bay Area is home to two of the world’s most toxic mushrooms – Amanita phalloides (death cap) and Amanita ocreata (western destroying angel).
The death cap and western destroying angel mushrooms contain amatoxins, a group of molecules that inhibit cellular metabolism in many animals. In mammals, the liver and kidneys are typically the first organs affected after ingestion. Symptoms don’t usually appear until up to 12 hours after consumption, beginning as severe gastrointestinal distress and progressing to liver and renal failure if treatment is not sought immediately.
“Both are robust mushrooms that grow near oak trees,” said East Bay Regional Park District Naturalist Trent Pearce, who is based in Tilden Regional Park and has documented several types of toxic mushrooms in East Bay parks. “Both are very dangerous and contain lethal toxins.”
Amanita phalloides (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. It fruits early in the fall, usually right after the first rains. Though 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.
Amanita ocreata (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 disappears with age, and a thin white sac at the base. It fruits from late winter into spring, and is associated exclusively with oaks. Unlike the death cap, it is a native California mushroom.
“We urge the public to be safe and be knowledgeable about toxic mushrooms,” said EBRPD Public Information Supervisor Dave Mason. “Park visitors should know mushroom collecting is not allowed anywhere in the East Bay Regional Park District.”
“Visitors should also keep their dogs away from them,” added Mason.
While the death cap and western destroying angel mushrooms are responsible for most cases of mushroom poisonings in California, deadly amatoxins can also be found in Galerina and Lepiota species, both which occur in the Bay Area as well.
Park visitors should remember that mushroom collecting is not allowed anywhere in the East Bay Regional Park District. If you are legally harvesting mushrooms elsewhere, learn these two species before any others and do not let them end up on your dinner table. Pet owners are encouraged to keep their animals under close watch during the winter months, and contact a veterinarian immediately if you suspect your pet has eaten a toxic mushroom.
Recommended reading: Mushrooms of the Redwood Coast, Siegal & Schwarz. 10-speed Press, 2016.
See also: bayareamushrooms.org
Text and photos by Trent Pearce, Naturalist, Tilden Nature Area
The East Bay Regional Park District is a system of beautiful public parks and trails in Alameda and Contra Costa counties east of San Francisco Bay, established in 1934. The system comprises 121,000 acres in 73 parks including over1,250 miles of trails for hiking, biking, horseback riding and nature learning.
Dave Mason, Public Information Supervisor