Deadly Mushroom Is at Home in the Santa Monica Mountains

Amanita phalloides, the death cap mushroom, is a highly toxic invader from Europe that can now be found growing under oak trees and in shady corners of gardens throughout the Santa Monica Mountains. Only a small percentage of wild mushrooms are deadly, and this harmless-looking mushroom is thought to account for 90 percent of mushroom-related fatalities. Photos by Suzanne Guldimann

Three white mushrooms appeared this week under an oak tree in a local garden—elegant, pale and perfect. At first glance, these mushrooms appeared to be harmless, but a faint greenish tinge to the caps warranted a closer look. Only a small number of mushroom species are deadly, and the vast majority of mushroom poisonings are caused by Amanita phalloides, the “death cap” mushroom. A greenish color is one of the identifying characteristics of this species.

It’s often said that there are old mushroom hunters, and there are bold mushroom hunters, but that there are no old, bold mushroom hunters. In this garden, the mushroom hunter’s interest isn’t cooking and eating the local fungi, it’s finding and removing any questionable mushroom before the family dog decides to sample it.

phalloides is a non-native that has spread throughout California and has made itself at home among the oaks of the Santa Monica Mountains. Eating just one of these mushrooms can cause permanent and potentially fatal liver damage. Even experts have mistaken these species for the common white edible mushroom they greatly resemble, and mushroom fanciers in pursuit of aren’t the only victims of this potentially fatal case of mistaken identity. Young children, dogs and even cats can become the victims of accidental poisoning. The North American Mycological Association (NAMA) cautions that dogs in particular may be attracted to A. phalloides, which can have a fishy odor.

Clinical toxicologist Rose Ann Gould, writing on the National Poison Control Center website (, cautions that amatoxins, the specific poison present in the death cap may cause “no effects right away, but can damage the liver; a liver transplant may be necessary to survive.”

A medical treatment for human victims involving intravenous silibinin, an antidote derived from milk thistle, may help prevent the liver from absorbing amatoxin. For dogs and cats IV fluids are the most common treatment. Accurate diagnosis and rapid treatment are critically important for all victims of mushroom poisoning.

Michael W. Beug, the Chair of NAMA’s Toxicology Committee, has studied mushroom toxicity for decades. On NAMA’s website he writes, “dogs may succumb to amatoxins more rapidly than humans may and so treatments employed without any delay are critical.” Symptoms are “characterized by a 6-12+ hour delay in symptoms followed by severe GI distress and refusal to eat or drink.”

Beug reports that a veterinary treatment that involves aggressive rehydration therapy together with drainage of the bile duct is promising, but that treatment needs to be swift. Beug stresses that it is important to bring a sample of the mushroom to the doctor with the patient to ensure identification and correct treatment.

Although it tends to grab headlines, mushroom poisoning is relatively rare considering how common death cap mushrooms are, and this is one hazard that is easily avoided.

In the Santa Monica Mountains most mushrooms appear during the rainy season, but A. Phalloides can pop up anytime soil conditions are moist enough. “May gray” mist and light precipitation, or garden irrigation can be enough to produce a crop of the mushrooms. Parents and pet owners can reduce the potential for mushroom exposure by removing any suspect mushrooms as soon as they appear. Mushroom enthusiasts should make sure that wild mushrooms have been identified by an expert before consuming. Simply avoiding white mushrooms in the wild is the best way to avoid accidental poisoning. Unlike some mushroom toxins, amatoxin is highly stable and remains lethally toxic even if the mushrooms are cooked.

“If in doubt, throw it out.”

The gills and spores of the death cap are very white, unlike similar edible species that are brown or pinkish. All death cap mushrooms grow from a cup-like volva at the base, so it is important to carefully remove the entire mushroom from the ground before attempting to identify it. Young death cap mushrooms have a veil or large skirt of white membrane on the stem that may be absent on older mushrooms. Dogs are reportedly attracted to death caps, possibly because the mature mushroom has a fishy aroma. Toddlers and young children are also at risk, but so are adult mushroom foragers who can mistake this attractive mushroom for one of several species that are safe to eat. It’s a good idea to remove any suspicious mushroom that sprouts in an area where children or pets play, and to make sure an expert inspects any mushroom gathered for food.


  • NAMA is a leading source of information on mushrooms of all types, poisonous and benign:
  • Berg recommends that anyone with a dog or cat suspected of consuming amatoxins contact; or (510) 219-0112 to find a vet with mushroom toxicity treatment experience.
  • If a child or an adult has eaten a potentially toxic mushroom, call Poison Control right away at (800) 222-1222. Poison Control specialists work directly with mycologists to determine the type of mushroom and can help provide guidance for emergency room doctors to ensure the victim receives the best treatment.


Suzanne Guldimann

Suzanne Guldimann is an author, artist, and musician who lives in Malibu and loves the Santa Monica Mountains. She has worked as a journalist reporting on local news and issues for more than a decade, and is the author of nine books of music for the harp. Suzanne's newest book, "Life in Malibu", explores local history and nature. She can be reached at

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