Top 20 Most Common Toxic or Poisonous Mushrooms in San Diego
As enthusiasts of the fungal world, one must tread with caution amidst San Diego's verdant landscapes and temperate climate. This unique environment is home to an intriguing mix of both beneficial and dangerous mycological species. We've dissected the top 20 most common poisonous mushrooms found in San Diego, ensuring you appreciate their beauty while avoiding their potential harm. With careful identification and a respect for nature, your mycological exploration can be rewarding and safe. Venture forth with knowledge and care!
* Disclaimer: Content feedback CAN NOT be used as any basis for EATING ANY PLANTS. Some plants can be VERY POISONOUS, please purchase edible plants through regular channels.
Most Common Toxic or Poisonous Mushrooms
1. False parasol
Though the false parasol appears unassuming, the species is famous—or, infamous—for its toxicity. It looks unfortunately similar to Agericus campestrus, a commonly eaten mushroom, but the false parasol can be distinguished by its highly unusual green spore print. Although they are no good to eat, they can be pretty to look at. The species may grow in ring-shaped groups in meadows and on forest floors in what are sometimes called "fairy circles."
2. Western jack-o'-lantern mushroom
The western jack-o'-lantern mushroom (Omphalotus olivascens) may be the most visually striking mushroom of the forest during day and night. During the day, brilliant large orange flat caps grow from both the ground and decaying stumps. At night, these mushrooms may glow in the dark, depending on location and maturity.
3. Flowerpot parasol
This tropical/subtropical mushroom is known to be toxic. If eaten it causes a very unpleasant stomachache with the risk of fatal complications. In temperate zones, flowerpot parasol is only found in hothouses and greenhouses, so the risk of accidental foraging is low, but it may occur with potted plants and indoor landscaping and pose a risk to curious children.
4. Wolf lichen
The thallus, or vegetative body, has a fructicose shape — that is, shrubby and densely branched — and a bright yellow to yellow-green, or chartreuse color, although the color will fade in drier specimens. Its dimensions are typically 2 to 7 cm (0.8 to 3 in) in diameter. The vegetative reproductive structures soredia and isidia are present on the surface of the thalli, often abundantly. 
5. Yellow stainer
The yellow stainer grows across North America and Europe and has been imported to Australia. It can be distinguished from other common white mushrooms by the bright chrome yellow color it turns when bruised. It is known to be poisonous, causing cramps, nausea, and purging. Unfortunately, it often gets accidentally eaten as it looks similar to several edible white mushrooms.
6. Shaggy parasol
The shaggy parasol grows singly or in groups from spring to fall. It can be found in lawns and gardens as well as the forest. It has a tendency to cause allergic reactions. Take care with identification as it is difficult to distinguish from the more deadly Amanitas.
7. Oak-loving elfin saddle
8. California agaricus
The california agaricus, found along portions of coastal California, is a toxic mushroom that is closely related to (and closely resembles) several sought-after, edible species, such as button mushrooms and white and brown field mushrooms. One distinguishing characteristic of california agaricus is that its flesh will begin to yellow when cut or bruised; unfortunately, this reaction is not always obvious. It is not deadly poisonous, but ingestion can cause gastrointestinal distress.
9. Mower's mushroom
The mower's mushroom, also referred to as the lawnmower's mushroom, is so named because it frequently crops up in lawns. The species is rather nondescript, and it is considered a member of the infamously hard-to-distinguish "Little Brown Mushroom" (LBM) family. While the mower's mushroom is not known to be toxic to humans or dogs, several of these close look-alikes are.
10. Poison pie
This toxic mushroom blooms on conifer and broadleaf forest floors around the northern hemisphere. It can appear singly, in tufted groups, or in fairy rings. The poison pie can be distinguished from its close relatives by the dark brown watery droplets that form in its gills. As the common name, "poison pie" implies, it is seriously toxic.
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