Armillaria ostoyae

[ Basidiomycetes > Agaricales > Marasmiaceae > Armillaria . . . ]

by Michael Kuo

In most areas of North America, Armillaria ostoyae can be separated from other species of Armillaria on the basis of its brown colors, the fairly prominent scales featured on its cap, and the well developed ring on its stem. It is usually found on conifers, and it is a ravaging parasite feared by forest managers across the continent.

In the northeast, from about New Hampshire to North Carolina, the hardwood-loving and apparently benign Armillaria gemina is a "morphologically inseparable" species--which means there is no way to distinguish it from Armillaria ostoyae by looking at it (with or without a microscope). However, the two species are unable to "mate" with each other, and are thus clearly distinct--though you may need a mycological laboratory and training in order to figure out which Armillaria you have collected.

Description:

Ecology: Parasitic and saprobic on the wood and roots of conifers (especially spruces) and, less frequently, hardwoods; causing a root rot (see this page for illustrations of tree damage); typically growing in dense clusters; summer and fall; widely distributed and common in northern and montane North America, but also appearing in other areas of the continent.

Cap: 3-20 cm; convex to broadly convex or flat in age; dry or slightly moist; dark brown to reddish brown or yellow-brown underneath tan to brown or blackish scales.

Gills: Attached to the stem or beginning to run down it; close; white or whitish; often developing pinkish hues and/or reddish brown spots and discolorations.

Stem: 6-15 cm long; 2-3 cm thick; more or less equal, or tapered to base; whitish, becoming brownish to nearly black toward the base; finely hairy; with a well developed whitish ring that may feature a brownish underside or edge; usually with yellowish mycelium near the base; attached to long black rhizomorphs that run through the wood.

Flesh: Whitish, sometimes becoming pinkish brown with maturity.

Odor and Taste: Taste mild to slightly bitter; odor not distinctive.

Chemical Reactions: KOH on cap surface negative.

Spore Print: White.

Microscopic Features: Spores 8-11 x 5-7 µ; smooth; more or less elliptical; inamyloid; with a prominent apiculus. Basidia basally clamped.

REFERENCES: (Romagnesi, 1970) Herink, 1973. (Moser, 1983; Berube & Dessureault, 1988; Berube & Dessureault, 1989; Breitenbach & Kränzlin, 1991; Hansen & Knudsen, 1992; Evenson, 1997; Volk, 2003; McNeil, 2006; Miller & Miller, 2006.) Herb Kuo 08180703.

Armillariella ostoyae is a synonym.

Further Online Information:

Armillaria ostoyae at Tom Volk's Fungi
Armillaria ostoyae at Common Tree Diseases of BC

© MushroomExpert.Com

Cite this page as:

Kuo, M. (2008, February). Armillaria ostoyae. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/armillaria_ostoyae.html