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.
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.
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
© Dianna Smith.
Figure 2. Several caps have fused laterally. Photo © Tom
Figure 3. The creamy white pore surface of Heterobasidion
annosum. Photo © Tom Volk.