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Species Information
Summary: Heterobasidion annosum group is recognized by the thin, brown to blackish brown crust on the often grooved or irregular cap surface, and cream-colored pores and margin. The pores reacting strongly with Melzer''s reagent. When growing flat without a cap, the margin is often very distinct and slightly raised. Dextrinoid skeletal hyphae can be distinctive (see MICROSCOPIC). |Heterobasidion occidentale is primarily on true fir, hemlock, and Douglas-fir, pores are round to elliptic with about 6% elongated to somewhat daedaleoid, and pore density 8.6 +/- 0.07 pores per square millimeter, whereas Heterobasidion irregulare is primarily on pine and juniper, pores about 10% or more radially elongated to somewhat daedaloid, and pore density 7.3 +/- 0.12 pores per square millimeter (Ginns(28) for British Columbia). |The Heterobasidion annosum group in North America appears to belong to two intersterility groups: "the p-type, which occurs mainly on pine, incense cedar, hardwood and brush, and the s-type, which infects other conifer species. The p-type will infect both p-and s-type hosts, whereas the s-type is restricted to s-type hosts." (Allen(1)). |Heterobasidion annosum sensu lato according to Garbelotto and Otrosina consists of at least 5 species, of which two occur in North America: Heterobasidion irregulare Garbelotto & Otrosina Fungal Biology 114: 20. 2010 (corresponding to the p-type) and Heterobasidion occidentale Otrosina & Garbelotto Fungal Biology 114: 20. 2010 (corresponding to the s-type). They measured mean pore density for H. occidentalis in 2 California sites as 8.6 per square mm with 6% of pores irregular and for H. irregulare in California and Georgia sites as 7.3 per square mm with 11% of pores irregular (irregularity of pores is affected by orientation however). |Heterobasidion occidentale is thought to occur in BC and its range is given as western North America from AK to southern Mexico. (Otrosina(1)). Heterobasidion irregulare also occurs in the Pacific Northwest, at least in BC, whereas Heterobasidion annosum is limited to Europe, (Ginns(28)).
Heterobasidion annosum group has been found in BC, WA, OR, ID, ON, AK, AL, AR, AZ, CA, CO, CT, DE, FL, GA, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, NH, NJ, NM, NY, PA, TN, TX, VA, VT, WV, Jamaica, and Europe (Gilbertson(1)), and also Asia and Australia (Breitenbach).
Cap: forming brackets, or bent outward from flat pore surface or often growing entirely flat on wood with pore surface exposed, caps up to 9cm x 15cm x 5cm, semicircular to long, narrow and shelf-like, irregular in shape, imbricate [shingled] or single, margin often wavy, rounded, sterile underneath; brown, blackish when old, margin colored the same; tomentose or bald, rough and irregular, indistinctly zoned and grooved, becoming incrusted, (Gilbertson), off-white, gray-brown, or dark brown, tinged red to blackish when old, (Lincoff(2)), margin thin, at first white (Lincoff(1)), usually brown to grayish brown with a pallid growing margin, but is sometimes reddish brown (and can be whitish when very young), (Arora), up to 15cm along wood and projecting 10cm, up to 3cm thick, gray-brown to dark brown, blackish when old, margin red-brownish, (Breitenbach)
Flesh: up to 1cm thick, corky; ivory, not zoned, "upper encrusted layer showing as a thin black line in section", (Gilbertson), white to pinkish cinnamon (Lincoff(2))
Pores: 4-5 per mm, circular to angular, walls thick and entire when young, becoming thin and torn when old; ivory white to pinkish cream; glancing [showing a change in appearance from dull to lustrous when the orientation to light is changed], smooth; tube layers up to 0.3cm thick each year, indistinctly stratified, colored as flesh and continuous with it, (Gilbertson), 2-5 per mm, circular to angular, often deformed, receding from old areas; white to yellowish, (Lincoff(2))
Stem: usually none, but may have a false stem
Chemical Reactions: flesh does not turn red with KOH
Odor: no particular odor (Lincoff(1)), strongly fungoid (Breitenbach)
Taste: no particular taste (Lincoff(1))
Microscopic: spores 4.5-6.5 x 3.5-8 microns [sic, but see other measurements below], nearly round to oval, minutely echinulate (spiny) or appearing smooth under light microscope, inamyloid, colorless, spores often difficult to find; basidia 4-spored, 16-22 x 5-6 microns, clavate, simple-septate at base; cystidia none; hyphal system dimitic: context generative hyphae 2.5-5 microns wide, colorless, "thin-walled, simple-septate, with occasional branching", context skeletal hyphae 3-5.5 microns wide, colorless, "thick-walled, nonseptate, dextrinoid, with occasional branching", trama hyphae similar, (Gilbertson), spores 3.5-5 x 3-4 microns (Lincoff(2)), spores 4.5-6 x 3.5-4.5 microns (Lincoff(1)), spores 4.5-6 x 4-4.5 microns (Breitenbach), "The dextrinoid staining of the skeletal hyphae in some basidiomata is hardly discernable and can take hours to develop", (Ginns(28))
Spore Deposit: white (Lincoff(2))
Habitat / Range
annual to perennial, on living and dead conifers, rarely on hardwoods, one of the major root pathogens in North American conifers, causing a white pocket rot of the roots and butt of living conifers, "pathogenic on living sapwood and causing mortality and windthrow of infected trees", (Gilbertson), also on some timbers (Lincoff(2)), trees attacked by the fungus easily blown down by the wind (Lincoff(1)), fruiting in spring and summer (Miller), typically "on the underside of logs, in cavities of trees, snags, and stumps, and often as a flat layer of tubes on the underside of woody substrates", (Trudell), summer to fall (Bacon)
Similar Species
Fomitopsis mounceae may be confused when its characteristic red marginal band is not present: F. mounceae 1) is generally smooth in its shape and surface (whereas H. ''annosum'' is rough, ridged and often irregular in outline), 2) is convex to hoof-shaped when old (as opposed to flattened for H. ''annosum''), 3) grows on live trees only when there is a wound big enough to expose the heartwood, 4) often grows high on trees (H. ''annosum'' always formed close to ground), 5) has distinctly stratified tube layers, 6) has flesh that turns red with KOH, 7) has smooth cylindric spores (not finely spiny nearly round to oval ones), and 8) has skeletal hyphae that are not dextrinoid (from several of the sources). Phellinus species have yellowish to orange to rust brown flesh, (Lincoff(2)). The rotted wood with black flecks is similar to the decays caused by Perenniporia subacida and Junghuhnia zonata, (Ginns(28)).
