Every mushroom expert repeats the same mantra: “Never eat a mushroom unless you can positively identify it.” Identification isn’t always easy, though. Mycologists have catalogued approximately 14,000 different mushroom species worldwide and classified them into a number of distinct genera. Each genus typically includes edible and inedible species, and many of these look similar. The genus Amanita is a case in point. It includes the poisonous Destroying Angel (Amanita virosa), the delicious Caesar’s mushroom (Amanita caesera) and the hallucinogenic Fly Amanita or toadstool (Amanita muscaria). How do you know which of these you’ve just come across?
A mushroom guide is a must for anyone interested in foraging for mushrooms. It’s helpful if the guide includes pictures of poisonous mushrooms, but because of the sheer number of possibilities, it’s even more helpful if the guide can zero in on a species as you enter information about the specimen you found. One such mushroom guide, posted by researchers from the University of Aarhus and University of Copenhagen, Denmark, is available online. It’s called MycoKey, and it isn’t the only such guide.
A number of factors enter into a positive identification. They include not just appearance, but also location, season and growing conditions. Even if you can’t make a positive identification, some general characteristics can alert you to the likelihood of a dangerous species.
Only about 3% of known mushroom varieties are poisonous, and the symptoms of poisoning can vary from gastrointestinal discomfort to liver failure and death, depending on the type of toxin ingested.
Acute liver failure from mushroom poisoning is relatively less common, but it does happen. And in the majority of cases, it’s because an amateur mushroom hunter or backyard forager misidentified a mushroom.
The most common dangerous mushrooms are those belonging to the Amanita genus, especially Amanita phalloides, aptly called “death cap” mushrooms. They contain toxic compounds called amatoxins that damage liver cells.
These mushrooms are white with umbrella-shaped tops and a cup at the base of their stem. They don’t look any more dangerous than supermarket varieties to an untrained eye, and they might actually taste good.
In less poisonous varieties, digestive symptoms of mushroom poisoning develop as early as 20 minutes to four hours after ingestion and normally pass after the irritant is expelled. But in the case of Amanita poisoning, initial symptoms might be delayed, Dr. Kapoor says, usually beginning 6 to 24 hours after ingestion.
Signs of mushroom poisoning
Nausea, vomiting, abdominal pain and diarrhea are the most common initial mushroom poisoning symptoms, but Dr. Kapoor says some patients show up at the hospital with low blood pressure, a manifestation of septic shock.
In the case of Amanita mushroom poisoning, symptoms are usually delayed for 6 to 24 hours, by which time the toxins have been completely absorbed. After an initial phase of digestive symptoms, the patient may appear to recover for two to three days, followed by relapse with liver and kidney failure, which could lead to massive bleeding and death.
Doctors use lab tests to confirm the presence of mushroom poisoning, but at the moment, there isn’t a specific drug to treat it. So doctors treat symptoms, starting with aggressive hydration with IV fluids.
Dr. Kapoor says there’s an experimental drug that’s shown promise in blocking liver cells from absorbing the poison. It’s called silibinin, an extract of the milk thistle plant, and although it’s not yet approved by the FDA in the U.S., doctors may be able to use it with special permission.
While some patients recover fully from mushroom poisoning, others require a liver transplant. A small portion of those poisoned by amatoxins die.
Two Tips to Help With Poisonous Mushroom Identification
If you come across a mushroom, a few defining characteristics can help you determine the possibility of it being poisonous. These aren’t definitive in that many edible species also display these characteristics, but if you notice them, they are a good indication that you should leave the mushroom alone. You might miss out on a delicious treat, but more important, you won’t die. And make no mistake: Death is a real possibility. Some 60 percent of cases involving Amanita and other species result in death. The tips are as follows.
Mushrooms with white gills are often poisonous. So are those with a ring around the stem and those with a volva. Because the volva is often underground, it’s important to dig around the base of a mushroom to look for it.
Mushrooms with a red color on the cap or stem are also either poisonous or strongly hallucinogenic. The most notorious red-colored mushroom is Amanita muscaria, which has been consumed for thousands of years to produce visions. In large doses, even this “magic mushroom” can be lethal. Other Amanita species also have this coloration, and they are far less benign.
Guidelines for Toxic Mushroom Identification
The consequences of misidentifying a mushroom are severe, so it’s important to ask yourself a series of questions before even touching one you’ve come across. Where is the mushroom growing? If it’s under a tree, what kind of tree is it? If it’s growing on wood, what kind of wood? For example, hens and chicks mushrooms are usually safe – even medicinal – but they have the potential to make you sick if they are growing on conifers, eucalyptus or cedar trees. You should also note whether the mushroom is growing alone or in a cluster, in sun or shade and what time of year it is.
If you feel confident enough to handle the mushroom – preferably using gloves – you can examine the gills, check the stem for rings and look for a volva. Press on the cap or make a small cut with a knife. Does the cap change color, and if so, what color? You might also cut off a small piece and smell it. Poisonous mushrooms often have an unpleasant, acrid smell, while benign ones smell refreshingly mushroomlike. You can also get information by cutting off the stem and placing the cap on a piece of paper gill-side down for a few hours to get a spore print. A white spore print is a telltale sign of an Amanita species.
Using an Online Mushroom Guide
It’s worth repeating the warning to never eat a mushroom until you can positively identify it. An efficient way to make a positive identification is to use a online catalogue. You can identify a dangerous species by looking at pictures of poisonous mushrooms, but if you can’t find any, navigate to a site that allows you to enter information about the specimen so you can zero in on the species. The search usually begins with the general shape of the specimen and its gill structure, and then proceeds to specifics, such as cap and gill color and texture, size and growing conditions. Once you’ve zeroed in on the genus and species, you can look up information about the edibility – or lack thereof – of the specimen.
Remember that mushrooms can be deceptively beautiful and dangerous at the same time. The aptly named Destroying Angel is a good example. Moreover, dangerous mushrooms can look like benign ones. For example, a sprouting Amanita looks like a young puffball, and you can’t tell the difference until you pierce the veil and look for gills inside, which mean the specimen is probably toxic. If you’re not sure, leave the mushroom alone.