Blue Cheese Polypore (Postia caesia)
Postia caesia
Visual Identification
What is Blue Cheese Polypore? A Complete Overview
Overview and Identification
Postia caesia, commonly known as the Blue Cheese Polypore due to its distinctive bluish tones and cheesy odor in maturity, is a saprophytic mushroom that grows primarily on dead wood. It is easily identified by its velvety cap, often powdery or felt-like in texture, sporting various shades of off-white, grayish blue, or sky-blue tinges. As it ages, the color tends to fade slightly, giving it a mottled or dusty appearance that makes it unique among wood-decaying fungi.
The fruiting body is typically fan-shaped to semi-circular, with margins that can be wavy or lobed. It usually grows in overlapping tiers or solitary rosettes, particularly on coniferous stumps or decaying logs. The pore surface underneath is white to cream-colored and features small, round pores that slightly bruise brownish-yellow on contact. The context of the mushroom is soft and watery when fresh, becoming hard and brittle once it dries out. Microscopically, it produces small, smooth, hyaline spores that are inamyloid and relatively uniform in shape.
Spore Print and Bruising Characteristics
The spore print of Postia caesia is white, matching many other members of the Polyporales order. Although it does not bruise vividly like some bolete species, the pore surface and context may subtly discolor or yellow when handled or exposed to air over time. One of its defining features is the absence of a well-developed stem, though in some specimens a rudimentary lateral stipe may be observed. The distinctive bluish hues make it relatively easy to identify once found in suitable habitats.
Taxonomic Classification
Historical and Cultural Significance of Blue Cheese Polypore
Historical and Ethnomycological Context
Postia caesia has not played a prominent role in human history or ethnomycological traditions. Its primary influence has been ecological rather than cultural. Unlike notable ethnofungi like Amanita muscaria or Psilocybe species, P. caesia lacks intoxicating, medicinal, or nutritional allure, which has rendered it relatively obscure in folklore.
That said, this species does appear in some European field guides and amateur mycology records dating back to the early 20th century. In regions like Scandinavia and the UK, it has been casually documented by naturalists interested in polypores and their role in wooded ecosystems. It occasionally features in public mushroom exhibitions as an example of forest microhabitats and the biodiversity of decomposers.
Modern Relevance
Its aesthetic appeal due to the blue hues sometimes earns it mention in art, photography, and nature journaling communities. The mushroom's nickname, "Blue Cheese Polypore," may derive not only from its coloration but also from the creamy, moldy smell produced by very mature specimens—conjuring the aroma of aged dairy products.
Where Does Blue Cheese Polypore Typically Grow?
Natural Habitat
Postia caesia is a saprobic fungus that thrives on dead or decaying wood, with a notable preference for coniferous trees such as fir, spruce, and pine. It can occasionally be found on hardwoods including birch and beech, though these instances are less common. This species plays a key role in the decomposition of lignin and cellulose and contributes significantly to forest nutrient cycling.
This polypore favors cool, moist environments, making dense woodlands and shaded forests its natural strongholds. It is often spotted after periods of sustained rainfall, growing on fallen logs, tree stumps, or heavily decayed trunks in advanced stages of rot. It is not uncommon to find them in clusters or developing tiered formations when conditions favor extensive mycelial colonization.
Geographic Distribution
Postia caesia is widely distributed across the Northern Hemisphere. In Europe, it's well-established from Scandinavia to the Mediterranean region, especially in mountainous and boreal zones. In North America, reports confirm its presence throughout Canada and the northern and western United States, including Pacific Northwest forests. It has also been sporadically reported in parts of Asia, including temperate Japan and Siberia. The mushroom's adaptability allows it to colonize a range of elevations, from lowland valleys to alpine areas, provided sufficient woody substrate and humidity are present.
When is Blue Cheese Polypore in Season?
Late Summer to Autumn
Is Blue Cheese Polypore Edible or Toxic?
Safety Information:
Toxicity and Risk Factors
Postia caesia is currently categorized as non-toxic but non-edible, primarily because of its unpalatable consistency rather than any intrinsic poisonous properties. No reported poisonings have been attributed to this species, and its close relatives also tend to be benign. Still, ingestion is discouraged unless absolutely certain of correct identification and origin.
Although not inherently harmful, consumption may cause gastrointestinal irritation in sensitive individuals, especially if gathered from polluted sites or consumed raw. Being a wood-decay fungus, it may accumulate heavy metals or environmental toxins from industrial areas, logging roads, or contaminated soils.
Risk of Misidentification
While not toxic itself, one of the key safety concerns is its superficial similarity to other bluish polypores – some of which may be mildly or moderately toxic. Foragers must verify identification with spore prints, microscopic analysis, and habitat information to confidently distinguish Postia caesia from potentially hazardous look-alikes. Consumption without positive identification by an experienced mycologist or forager is not advised.
Precautions and Interactions
Known Drug Interactions
Given the lack of documented medicinal usage and the fact that Postia caesia is generally not consumed, there are no known drug interactions for this mushroom. It is not known to interfere with any pharmaceutical medications or medical treatments.
However, as a standard precaution in mycology, individuals attempting experimental or anecdotal uses should avoid combining it with medications—particularly immunomodulators, anticoagulants, or liver-metabolized drugs—until more is known. As Postia caesia contains unknown bioactive compounds, its safety in medical contexts remains unestablished.
General Considerations
In conclusion, no adverse drug interactions have ever been reported, but the lack of usage history and research should give cause for cautious inaction until further studies emerge.
What Mushrooms Look Like Blue Cheese Polypore?
Commonly Confused Species
Several other fungi resemble Postia caesia, making correct identification especially important for foragers, photographers, and mycologists. Below are the main lookalike species along with ways to differentiate them:
- Trametes versicolor (Turkey Tail): This popularly known polypore has a multicolored concentric zoning pattern on the cap, distinguishing it from the more monotone blue-white hue of Postia caesia. Trametes versicolor has a notably thinner fruiting body and lacks the powdery surface texture seen in Postia.
- Postia subcaesia: A very close relative with nearly identical morphology, but often smaller in cap width and generally more drab in coloration. They can sometimes be differentiated microscopically by spore size and shape, although field identification may be difficult.
- Bjerkandera adusta: Similar in overall shape and habitat, especially on rotting wood. However, Bjerkandera adusta tends to have darker gray to brown tones and lacks the bluish shades seen in Postia caesia. The texture also differs, with B. adusta more leathery and rubbery compared to the softer surface of P. caesia.
Being aware of these lookalikes is crucial for field identification and preventing erroneous data collection by citizen scientists.
Safety Note: Always use proper identification methods and consult expert mycologists when foraging. Misidentification can have serious health consequences.
Disclaimer: This information is for educational and identification purposes only. Never consume wild mushrooms without expert identification. Always consult with qualified mycologists and healthcare professionals. Foraging and consumption of wild mushrooms carries inherent risks.