Heterobasidion annosum

Scientific name:  Heterobasidion annosum (Fr.) Bref.
Derivation of name:   Heterobasidion with "with different
or variable basidia"; annosum means "aged" or "full of years"
(perennial) although the fungus is sometimes an annual.
Synonymy:   Fomes annosus (Fr.) Cke.
Common names:   Conifer-base polypore.
Phylum:   Basidiomycota
Order:   Russulales
Family:   Bondarzewiaceae
Occurrence on wood substrate:  Parasitic and saprobic;
solitary or overlapping at the base of stumps, on dead trunks
and logs, and on the roots of living conifers, rarely on
deciduous trees; year-round. 
Dimensions: Caps up to 15 cm wide, 9 cm long, and 5 cm
thick. Caps sometimes fusing into longer rows.  Fungus
sessile, effused-reflexed, or resupinate.  
Upper surface:  Young caps grayish-white, becoming gray-
brown to blackish-brown with age; rough and irregular;
concentrically zoned or furrowed; hairy to glabrous.
Pore surface: White to cream; pores 2-5 per mm.
Edibility: Inedible.
Comments: Heterobasidion annosum is a major root rot
pathogen of conifers in North America.

More information at RogersMushrooms.com: 


Figure 1. Heterobasidion annosum often has a wavy
margin. Photo © Dianna Smith.


Figure 2. Several caps have fused laterally. Photo © Tom
Volk.


Figure 3. The creamy white pore surface of Heterobasidion
annosum
. Photo © Tom Volk.

 

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