Each year, winter rains bring a variety of mushrooms out at Midpen preserves. The multitude of fungi are amazing, but some are deadly poisonous. Picking and eating wild mushrooms can kill you! Mushroom collecting is not allowed anywhere in Midpeninsula Regional Open Space District. Please leave mushrooms alone for other visitors to see and for the safety of you and your family.
The Bay Area is home to two of the world’s most toxic mushrooms – Amanita phalloides (the Death Cap) and Amanita ocreata (the Western Destroying Angel). Both grow near oak trees and contain lethal toxins.
Amanita phalloides (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. 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 (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 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.
Both of these species 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 about 12 hours after consumption, beginning as severe gastrointestinal distress and progressing to liver and renal failure if treatment is not sought immediately.
While these two species are responsible for most cases of mushroom poisonings in California, deadly amatoxins can be found in Galerina and Lepiota species as well, both of which occur in the Bay Area.
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.