What You Should Know
Postia caesia can be distinguished by relatively small white fan-shaped fruit bodies that are soft and fibrous and stain blue when bruised. It is the only soft, white bracket fungus in California that bruises blue, so it is easily distinguished from other polypores.
This mushroom is widespread in Britain, Ireland, and Europe. It is also recorded in parts of Asia and North America.
Recent work has shown that Postia ceasia is not known to occur in North America. A candidate name for our species is Postia simulans (P. Karst.) Spirin & B. Rivoire.
Postia caesia Mushroom Identification
The fruit bodies are typically 1 to 5 cm across and up to 1cm thick, and the upper surface is covered in fine hairs and radial wrinkles that create a slightly wavy margin. The upper surface is white initially but develops a blue-gray tinge as it matures, and it also blues fairly soon after being handled.
Tubes and Pores
The pores are white and spaced 4 to 6 per mm.
Sausage-shaped, smooth, 4-5 x 0.7-1.0µm; amyloid.
Very pale blue.
Odor and Taste
Mild odor; very little taste.
Brackets are visible throughout most of the year, but they release their spores in late autumn.
Postia caesia Look-Alikes
Similar but where injured turn ochraceous to reddish-brown, not blue.
Whitish to grayish, lacks any blue coloration, with a slightly firmer texture.
Cyanosporus subcaesius (syn. Postia subcaesia) and Postia alni
Both more often associated with broadleaf trees rather than conifers, have rather different blueing characteristics, and produce narrower spores.
Postia caesia Taxonomy and Etymology
In 1794 German botanist and mycologist Heinrich Adolph Schrader (1767 - 1836) described this species and established its basionym when he gave it the binomial name Boletus caesia.
The Conifer Blueing Bracket was transferred to its present genus in 1881 by the Finnish mycologist Petter Adolf Karsten (1834 - 1917), at which point its scientific name became Postia caesia.
Synonyms of Postia caesia include Boletus caesius Schrad., Polyporus caesius (Schrad.) Fr., Leptoporus caesius (Schrad.) Quél., Tyromyces caesius (Schrad.) Murrill, and Oligoporus caesius (Schrad.) Gilb. & Ryvarden.
Postia, the genus name, was established by Elias Magnus Fries in honor of the Swedish naturalist Hampus von Post (1822 - 1911).
The specific epithet caesia means sky blue and is a reference to the blue-gray color of the upper (infertile) surface of mature specimens of this bracket fungus.
Postia caesia Video
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