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Fall Mushrooms of the Diablo Region

Updated: Jan 8, 2019

Mount Diablo Interpretive Association


Rain has come late to the Bay Area this year which has delayed the appearance of our seasonal mushrooms. On average our “mushroom season” begins in October, and yet we find ourselves here in December just now seeing fungal activity.

It takes a few quality rains before mushrooms are cued to appear. To understand the process of mushroom growth and why they are just now being observed, it’s important to recognize the process of fungal development. This requires us to look at the whole organism which not only includes the mushroom, but also a series of white filaments known as “mycelium.”

Mycelium most commonly appears as white threads that are sometimes visible at the base of mushrooms. Mycelium can sometimes be mistaken for the “roots" of mushrooms; they resemble roots and descend from the base of a mushroom into the ground or woody substrate.

What few people realize is that these white filaments are the actual fungal organism itself. Mushrooms are just the “fruiting bodies” or reproductive organs of mycelium. They are merely the tip of the iceberg, with the majority of the organism living below it in the form of mycelium.

The mushroom’s sole purpose is to spread spores so that the mycelium--the fungus itself--can survive. When fungi are ready to reproduce, thousands of the filaments that form the mycelium pull together to create a mushroom. That mushroom develops spores which are released into the air giving the fungus a chance to reproduce.

Water is the primary catalyst for fungal growth and low saturations equates to dormant mycelium. Though winter is fast approaching and temperatures are dropping, the late rain is just now coaxing our traditional fall mushrooms into appearance. The substrates on which mushrooms grow are becoming increasingly saturated, prompting fungal activity.

The following are the most common fall mushrooms that are now emerging:

Oyster Mushrooms (Pleurotus species) grow on hardwoods, commonly in clusters. They are fan-shaped, range from white to gray, and have lines of “gills”--the soft plate-like structures that release spores--visible on the underside. Oyster mushrooms are a prized edible though there are reports of allergic reactions.

Jack-o-Lanterns (Omphalotus olivascens) grow on hardwoods and are most commonly found in clusters. They are fan shaped, have gills on the underside, and range from neon orange to brown in color. Jack-o-lanterns are poisonous (but not fatal), with extreme stomach upset as the result of consumption. This fungus is capable of bioluminescence, a glow-in-the-dark phenomenon that is the result of a chemical reaction taking place (not solar activation).

Turkey Tails (Trametes versicolor) grow in clusters on dead wood. Like the name suggests, this fungus grows in a fan shape resembling the tails of a turkey. Each “tail” exhibits shades of white, brown, and occasionally purple and dull green concentric rings radiating from the center. Most mushrooms have a seasonal lifespan, but turkey tails remain intact year round and simply go dormant in the summer time. When it rains, turkey tails rehydrate and restart their growing and sporulating process. Turkey tails are often used in soups and are said to contain strong medicinal properties.

Witches Butter (Tremella aurantia) is a wildly unique, brain-like fungus that grows alone or in clusters on dead hardwood. Squishy, slimy, gelatinous, and bright yellow, witches butter is one of several jelly fungi that grow in the Bay Area. Our local species parasitizes other fungi, especially the turkey tail lookalike “hairy curtain crust” (yes, that is in fact the common name). Despite its unpalatable appearance, witches butter is used as a thickener in soups.

Death Caps (Amanita phalloides) are as ominous as they sound. These mushrooms commonly appear in the fall, though there have been years when few have been discovered. Death caps grows from soil and leaf litter primarily under oak trees. They form in the traditional mushroom shape with coloration that ranges from dull yellow to olive green. Death caps resemble a few edible mushrooms which make them especially dangerous for foragers. Responsible for 14 poisonings in the Bay Area in 2016, the death cap destroys the liver, and without an immediate liver transplant, consumers face death.

Start looking--there are mushrooms out there to be found! Though it’s hard to predict fungal activity, with our late start this year it’s quite possible that the entire 2018-19 mushroom season could be delayed. Stay tuned for more mycological updates!

Learn more about the Mount Diablo Interpretive Association here.

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