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Grey-Brown Sap Rot

Cryptoporus volvatus (Peck) Shear
(= Polyporus volvatus Peck)

Basidiomycotina, Aphyllophorales, Polyporaceae

Hosts: Grey sap rot has been reported from a wide range of coniferous hosts but is most common in bark beetle- and fire-killed Douglas-fir. In B.C., the fungus has been reported on amabilis, grand, and subalpine fir, Sitka and white spruce, lodgepole, ponderosa and western white pine, Douglas-fir, and western hemlock. Elsewhere in North America it has also been found on black and Englemann spruce, California incense cedar, and western larch.

Distribution: This fungus is widely distributed throughout the range of its hosts in B.C.

Identification: The fruiting bodies are annual, leathery, pouch-like structures, up to 4 cm wide x 5 cm high x 4 cm deep (Figs. 47a, 47b). The upper surface is smooth, and yellow to light brown turning white with age. The brown poroid lower surface is at first covered with a hard membrane continuous with the upper surface, hence the common name "pouch fungus." Later an opening forms at the base of the membrane to permit the release of the spores.

The fungus causes a cream to light grey discoloration in narrow bands in the outer sapwood; the discoloration is particularly evident in a radial or tangential section. In the advanced stage, the affected wood is light brown, cubical and crumbly.

Microscopic Characteristics: Hyphae in the context of the fruiting body are thin-walled with clamps at all septae. Basidiospores cylindric, hyaline, smooth, IKI-, 12-16.5 x 4.5 µm. Growth in culture moderate to slow, mat white, odour pungent, laccase positive. Stalpers: 1 3 (7) (9) (11) 13 (14) (16) (17) (18) 30 (36) 39 42 44 45 (47) 52 53 (54) (79) 80 90 (94).

Damage: Grey sap rot develops rapidly in dead standing trees but is quite superficial, limited to the outer 1-2 cm of sapwood. As a result, little or no board-foot volume loss is associated with this decay.

Remarks: Fruiting bodies usually develop the year after tree death occurs, and often form by the hundreds up the stem (Fig. 47c). On Douglas-fir, C. volvatus is often associated with old bark beetle galleries and can be used as an indicator of bark beetle kill. Sporophores of Cryptoporus volvatus could be confused with immature conks of other polypore fungi. The latter, however, are solid rather than "pouch-like." Insects have been shown to play a role in the dissemination of C. volvatus basidiospores.


Borden, J. H. and M. McClaren. 1970. Biology of Cryptoporus volvatus (Peck.) Shear (Agaricales, Polyporaceae) in southwestern British Columbia: distribution, host species, and relationship with subcortical insects. Syesis 3: 145-154.

Gilbertson, R. L. and L. Ryvarden. 1986. North American Polypores. 1:220. Fungiflora, Oslo.


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Figures 47a: Fruiting bodies of C. volvatus, some dissected longitudinally to show the spore-producing surface "hidden" by a membrane.




Figure 47b: Fruiting bodies of C. volvatus, some dissected longitudinally to show the spore-producing surface "hidden" by a membrane. The pore through which spores are released is visible.




 Figure 47c: Fruiting bodies on the stem of a dead Douglas-fir.