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Brown Cubical Rot of Birch

Piptoporus betulinus (Bull.:Fr.) P. Karst.
(= Polyporus betulinus (Bull.:Fr.) Fr.)

Basidiomycotina, Aphyllophorales, Polyporaceae

Hosts:Piptoporus betulinus is restricted to birch; white birch in B.C. and yellow birch elsewhere.

Distribution: This fungus is found throughout the range of birch in the province.

Identification: The fruiting bodies are annual, leathery, with a short, stout stipe, and a cap up to 15 cm deep, x 25 cm wide x 6 cm high (Fig. 23a). The upper surface is light brown, becoming darker brown and scaly, with a margin that extends below the pore surface. The pore surface is white, becoming light brown and slightly tooth-like with age (Fig. 23b), pores circular, 3-5 per mm. Context white, easily separating from tube layer when fresh.

Decayed wood is yellowish-brown and cracks into cubes with thin white mycelial mats forming in the cracks. Wood in advanced stages of decay is very light in weight and easily crumbles to powder.

Microscopic Characteristics: Hyphae in the context of the fruiting body of two types: thin-walled, hyaline with clamp connections, and thick-walled, aseptate Basidiospores cylindric, allantoid, hyaline, smooth, IKI-, 5-6 x 1.5-1.7 µm. Growth in culture moderately rapid, mat colourless to white, forming compact balls of mycelium on surface of medium, chlamydospore-like swellings, laccase negative. Stalpers: (6) (7) (12) (13) 14 17 19 21 (22) 30 (31) 80 83 (85) (88) 89 (93).

Damage:Piptoporus betulinus is often present in dead branches of dying trees. After trees die, rot develops in the bark and sapwood, and generally spreads to the centre of the trunk. Infected wood decays rapidly; laboratory studies have shown reduction of wood density of 30-70% in four months.

Remarks: Piptoporus betulinus is one of the few brown rotting fungi that only attacks hardwoods. Although it is restricted to birch hosts in nature, other tree species such as pine, spruce, and poplar have been successfully inoculated in lab and field experiments.


Gilbertson, R. L. and L. Ryvarden. 1987. North American Polypores. 2:633. Fungiflora, Oslo.


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Piptoporus betulinus fruiting body - Click on the image to see a larger version

Figure 23a: Piptoporus betulinus fruiting body on a dead standing birch stem.



Older fruiting bodies on a fallen birch stem - Click on the image to see a larger versionFigure 23b: Older fruiting bodies on a fallen birch stem.