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Pitted Sap Rot

Trichaptum abietinum (Dickson:Fr.) Ryvarden
(= Hirschioporus abietinus (Dickson:Fr.) Donk)
(=Polyporus abietinus (Dickson:Fr.) Donk)

Basidiomycotina, Aphyllophorales, Polyporaceae

Hosts: Pitted sap rot is found in a wide range of coniferous hosts. In B.C., it has been reported on amabilis, grand and subalpine fir, western larch, white, black, and Sitka spruce, lodgepole, ponderosa, Scots, white-barked, and western white pine, Douglas-fir, western redcedar, western hemlock, Arbutus, and cherry. Elsewhere in North America it has also been found on mountain hemlock, California incense cedar, Chamaecyparis thyoides, beech, juniper, Sequoia, Engelmann spruce, and Taxodium.

Distribution: This fungus affects trees in all regions of the province.

Identification: Fruiting bodies rarely form on living trees but may be produced in great abundance on dead trees and forest litter. They are small (1-3 cm across), annual, thin, effused-reflexed, or shelf-like, forming abundantly in bark crevices. The upper surface is zoned, light grey and somewhat hairy in texture. On older specimens the upper surface may appear green from algal growth, or black (Fig. 49a). The lower surface is purple when fresh turning light brown with age. Pores are angular, 4-6 per mm, and with maturity the tissue between the pores tends to become elongated and torn into irregular spines or ridges (Figs. 49b, 49c).

In the early stage of decay, the wood becomes light-yellow to tan and soft. In the advanced stage, small pits develop, elongated in the direction of the grain, which may at first be filled with white fibrous material but later become empty. The cross section of the decay has a honeycomb appearance.

Microscopic Characteristics: Skeletal hyphae in the context of the fruiting body thick-walled, nonseptate, contextual generative hyphae thin-walled with clamps. Basidiospores cylindric, slightly curved, hyaline, smooth, IKI-, 6-7.5 x 2.5-3 µm. Growth in culture moderately rapid, mat white, translucent, laccase positive, clamps. Stalpers: 1 3 (7) (8) (11) 13 14 17 (18) 19 (21) 22 30 39 42 44 (45) (46) 48 52 53 54 57 72 (81) 82 83 (89) 90 (94).

Damage: The fungus is of primary importance as a deteriorating agent but is also capable of causing sap rot and heart rot in living trees. Extensive decay of sapwood is indicated by the presence of fruiting bodies. It has been reported to have caused decay in unseasoned wood in service.

Remarks: The decay caused by this fungus is restricted to the sapwood; fruiting bodies often form a complete ring on the sapwood of the cut ends of logs. The fruiting bodies of T. abietinum could be confused with those of Stereum sanguinolentum. The hymenium of the latter will turn red when bruised. Earlier taxonomic treatments of T. abietinum were broad, and included fungi now recognized as separate species (T. fuscoviolaceum and T. laricinum). Many reports of T. abietinum may be these species.


Gilbertson, R. L. and L. Ryvarden. 1987. North American Polypores. 2:768. Fungiflora, Oslo.


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Figure 49a: Old fruiting bodies of T. abietinum with algae growing on the upper surface.



 Figure 49b: A mass of fruiting bodies in typical abundance on a dead Douglas-fir stem.






 Figure 49c: The ridged pore layer of T. abietinum fruiting bodies.