Persoonia 11(4): 423. 1982.
Common Name: none
Synonyms: Tyromyces fragilis (Fr.) Donk; Oligoporus fragilis (Fr.) Gilb. and Ryvarden; Polyporus fragilis Fr.
Fruiting body annual, effused-reflexed, sessile, elongate fan-shaped, 3.0-7.0 cm long, 2.0-3.0 cm wide, 0.5-1.0 cm thick; margin wavy, sometimes over-lapping the tube layer; upper surface white, tomentose, becoming matted in age, azonate, bruising or weathering tawny-brown to vinaceous-brown, eventually dark rusty-brown; context when young soft, white, resilient, up to 0.5 cm thick, discoloring like the upper surface, in age rigid, brownish; odor slightly pungent; taste somewhat bitter.
Pores 3-4 per mm, whitish, round to angular, bruising vinaceous-brown to reddish-brown, dissepiments thin, becoming torn to dentate with age; tubes 4.0-5.0 mm long, whitish, bruising like the pores.
Spores 4.0-5.0 x 1.0-1.5 µm, cylindrical in face view, sausage-shaped in side-view, smooth, thin-walled, with prominent granular inclusions, hilar appendage not obvious, inamyloid, not dextrinoid; spores white in deposit.
Solitary or in small groups, imbricate or in horizontal lines on conifer logs and branches; fruiting from mid to late winter.
Postia fragilis is a fairly unremarkable polypore: small, whitish, soft-textured when young, with a matted-tomentose upper surface, and annual fruiting habit. Its most obvious feature, bruising reddish-brown, is mimicked by three other polypores, Parmastomyces transmutans, Amylocystis lapponica and Leptoporus mollis. These species can be separated in the field by their tendency to bruised reddish-brown directly rather than through an intermediate tawny-brown stage. With a microscope Parmastomyces transmutans differs in having dextrinoid spores, Amylocystis lapponica by amyloid cystidia, and Leptoporus mollis by the lack of clamped septate, generative hyphae.
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