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Species Information
Summary: {See also Amylocystis lapponica, Leptoporus mollis, Postia fragilis Table.} Features of Postia fragilis are the bracket-like or shelf-like, whitish to buff fruitbodies that turn reddish brown on bruising or drying, and its microscopic characters. The current name in the online Species Fungorum, accessed April 20, 2020, is Fuscopostia fragilis, but the current name in Mycobank, accessed the same day, is Postia fragilis.
Postia fragilis is found in BC, WA, OR, ID, AB, NB, NS, ON, PQ, AK, AZ, CA, CO, FL, MA, MD, ME, MI, MN, MT, NC, NH, NJ, NM, NY, PA, TN, UT, VA, WI, and WY, (Gilbertson), and Europe, Asia, and Australia, (Breitenbach).
Cap: up to 4cm x 6cm x 1cm, bracket-like or bent outwards to form cap from pore surface growing flat on wood, dimidiate [semicircular] or elongated; whitish to buff, turning reddish brown on bruising or drying, not zoned; tomentose to bald, (Gilbertson), 2-10cm broad, shelf-like or bracket-like, elongated or fan-shaped, "soft and spongy or watery when fresh, rigid and brittle when dry"; white, becoming reddish to pinkish red when old, "staining yellowish, then rusty to reddish when handled"; covered with soft white hairs, (Arora), 2-6cm along wood, projecting 2-4(5)cm, 0.5-1cm thick at attachment, bracket-like to fan-shaped; "yellow-ocher to orange-brownish", spotting brownish when handled, "shallowly undulating-tuberculate, somewhat radially fibrillose, finely tomentose and not or weakly zoned"; margin somewhat wavy, +/- sharp, white to ocherish, (Breitenbach)
Flesh: up to 1.5cm thick, fibrous; white, drying brownish, not zoned, (Gilbertson), soft when fresh; white, discoloring like cap surface, (Arora), flesh 0.2-0.8cm thick, "succulent, fibrous, elastic", (Breitenbach)
Pores: 5-6 per mm, circular to angular, with walls that become thin and torn; whitish to buff, becoming reddish brown on bruising or drying; tube layer up to 0.4cm thick, darker than flesh, (Gilbertson), 3-5 per mm, "white, quickly bruising yellowish, then rusty-reddish"; tube layer 0.2-0.8cm thick, (Arora), 2-4 per mm, angular to labyrinthine [maze-like], usually decurrent onto wood; white, spotting brownish when handled; tube layer 0.2-0.5cm thick, (Breitenbach)
Microscopic: spores 4-5 x 1-1.5 microns, cylindric, mostly curved, smooth, inamyloid, colorless; basidia 4-spored, 13-20 x 4.5-5.5 microns, clavate; cystidia none; hyphae monomitic, hyphae of context 3-7 microns wide, colorless in KOH, thin-walled or thick-walled, occasionally branched, with clamp connections, hyphae of trama 2.5-4 microns wide, colorless, thin-walled or thick-walled, often branched, with clamp connections, (Gilbertson), 4-5 x 1-2 microns, cylindric to sausage-shaped, smooth, (Arora), spores 4.5-6 x 1.5-2 microns, cylindric, somewhat allantoid, smooth, colorless, with droplets, (Breitenbach), spores 4-5 x 1.0-1.5 microns, allantoid, hyphae 3-7 microns wide, walls thin to thick, hyphae on cap surface "mostly thin-walled in agglutinated pale yellow to pale brown strands", (Ginns(28))
Spore Deposit: whitish (Arora)
Habitat / Range
annual, single, on dead conifers, rarely on Populus; associated with brown cubical rot of dead conifer logs and slash, (Gilbertson), single "or in groups or fused clusters on rotting conifers", (Arora), summer to fall (Buczacki)
Similar Species
Amylocystis lapponica fruitbodies "resemble robust specimens of O. fragilis and also show the reddish-brown color change on bruising. The capitately incrusted amyloid cystidia of A. lapponica make it distinctive microscopically" - spore size is larger and pore size is slightly larger for A. lapponica, (Gilbertson). A. lapponica has cylindric spores 8-11 x 2.5-3.5 microns, clamp connections, and amyloid metuloids, Leptoporus mollis has allantoid spores 5-6 x 1.5-2 microns, no clamp connections, and no cystidia, and Postia fragilis has allantoid spores 4-5 x 1-1.5 microns, clamp connections, and no cystidia, (Ginns(25)). Sarcoporia polyspora also stains reddish brown - it has elliptic to cylindric spores 5-7 x 2.5-4.0 microns, has clamp connections, and lacks cystidia. Postia lateritia, rarely reported, has larger pores (3-4 per mm), soft context, slightly larger pores measuring 4.5-6.3 x 1.0-1.8 microns, thick-walled cap hyphae (thin-walled in P. fragilis), and scattered gloeoplerous hyphae (Ginns(28)). See also SIMILAR section of Postia leucomallella.
