I found clusters of white, petal-shaped mushrooms on the north side of a tree in Whatcom Falls Park. They clung to a dying tree’s trunk, in a graceful upward sloping pose, as if reaching for the sky. My boyfriend announces they are Oysters and with steadfast confidence insists there are no similar looking mushrooms to confuse them with. I’m not as confident in his mushroom identification skills—and proper identification is a matter of life or death—so I snapped a few photos and dove into a research hole as soon as I got home. Here’s what I’ve learned:
“Oyster mushroom” is actually a term used for a collection of closely related species. The mushrooms we saw were the classical Pleurotus ostreatus (which can be abbreviated to P. ostreatus), also referred to as the Pearl Oyster, Tree Oyster, and Tree Mushroom. Interestingly, Oyster mushrooms are one of the few known carnivorous mushrooms*—a fact I had to look up in multiple sources before I believed it. It turns out that Oyster mushrooms can sense the location of nematodes (also known as roundworms)[1], and emit chemicals to attract their prey. When a nematode gets close enough, it is paralyzed by a neurotoxin on tiny nobs that stick out from the mushroom’s hyphae[2]—I like to think of hyphae as the tentacles of a mushroom. Hyphae grow into the paralized nematode’s body and enzymatically digest it from the inside out.[1] Oyster mushrooms have developed this adaptation to supplement their diet of dead wood (rich in cellulose and lignin, but lacking nitrogen-containing protein).
In addition to eating nematodes, it turns out oyster mushrooms can digest petrochemicals as well. When a Seattle company ran an experiment covering oyster mushrooms in oil, most of the oil was consumed in three weeks, with more oysters popping up on what remained.[4] In an Washington Sate Department of Transportation experiment (conducted right here in my current hometown of Bellingham, WA), oyster mushrooms restored life to diesel fule contaminated soil after four weeks.[5]
Are they edible?
Multiple sources confirm that Pleurotus ostreatus are edible including:
- The Mycological Society of San Francisco in their article “Oyster Mushroom” http://www.mssf.org/cookbook/oyster.html
- “All That the Rain Promises, and more… A Hip Pocket Guide to Western Mushrooms” by David Arora
- “The Complete Guide to Edible Wild Plants, Mushrooms, Fruits, and Nuts” by Katie Letcher Lyle
Mushrooms that look similar
Despite my boyfriend’s confidence, it turns out there are several mushrooms that are similar in appearance to P. ostreatus.
Pleurocybella porrigens
Pleurocybella porrigens, or “angels’ wings,” are often described as the “slender, smaller, short-stemmed relatives of P. ostreatus”[3]. Angels’ wings are generally considered to be edible, though they’ve been linked to a few deaths [4], which scientists believe were caused by consuming unusually large quantities of this mushroom.
Pleurotus pulmonarius
Pleurotus pulmonarius is a mushroom of many names. It is known as the Indian Oyster, Italian Oyster, Phoenix Mushroom, and Lung Oyster. It looks a lot like P. ostreatus, but is much smaller, paler, and tends to have a longer “stem”. It also prefers warmer weather than P. ostreatus.
Pleurotus populinus
Pleurotus populins is known as the aspen oyster mushroom, and can be found on the dead wood of aspen and cottonwood trees.
When they grow
According to the Mycological Society of San Francisco, P. ostreatus appear in the Fall, while the “The Complete Guide to Edible Wild Plants, Mushrooms, Fruits, and Nuts” says you can see them growing from Spring to Fall.
In Whatcom County, I’ve personally seen them starting to grow the last week of April and exploding towards the end of the first week of May.
What they grow on
I’ve seen them growing on the sides and tops of dead tree stumps and up the side of trees, which I’m guessing are in the process of dying since the Oysters are present.
Where to find them
They seem to be relatively common in Whatcom County (compared to other edible mushrooms). I’ve seen them growing all around Bellingham, Washington, in Larrabee State Park, Whatcom Falls Park, and off the Samish Crest Trail.
*Technically, I’d refer to them as omnivorous, since they also consume wood
Sources
- California Mushrooms: The Comprehensive Guide Loc 410
- When Mushrooms Attack Northernwoodlands.org
- http://www.mssf.org/cookbook/oyster.html
- https://namyco.org/pleurocybella_toxin.php
- https://www.discovermagazine.com/environment/how-mushrooms-can-save-the-world