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The Genus Armillaria  

[ Basidiomycota > Agaricales > Physalaciaceae . . . ]

by Michael Kuo

Until recently, Armillaria was a rather large genus, containing over 200 species. The previously accepted definition of the genus included terrestrial mushrooms with white spore prints and a partial veil forming a ring. Wood-eating white-spored mushrooms with rings were placed in Armillariella, and Catathelasma species had double-layered veils, coniferous habitat, and large, hard fruiting bodies.

However, a series of publications over the past 10 or 20 years has changed all of the above. Armillaria is now much smaller, and most of its former species have been spread out through 25 other genera (most notably, from an amateur mushroomer's standpoint, Tricholoma). In the wake of the storm, Armillaria includes only white-spored, wood-rotting mushrooms with gills that are attached to the stem or run down it; most species are parasitic, and many form visible black rhizomorphs in the wood. (See the page for Armillaria mellea for more information on the Armillaria shake-up.)

In North America, the current definition leaves under a dozen species belonging to Armillaria. The authoritative key to these species, by Tom Volk, can be found at his wonderful Web site. The key below is my adaptation; it emphasizes macroscopic features and ecological factors.


Armillaria mellea

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Key to 8 Species of Armillaria in North America

1.Stem without a ring or cobweb-like ring zone.

1.Stem with a ring or ring zone.

2.Mature cap with prominent scales.

2.Mature cap smooth, with scattered fine hairs, or with tiny scales, but without prominent scales.

Note: The two species in Couplet 3 cannot be reliably separated by comparing physical features. According to Volk (2005), they "can usually be distinguished by geography, but in areas where the ranges of the two species overlap (such as in New Hampshire south to western North Carolina) they can be distinguished only in cultural studies."

3.Found on hardwoods; distributed from the Appalachian Mountains eastward; rare; benign.

Armillaria gemina
(see Armillaria solidipes)

3.Found primarily on conifers; widely distributed in northern North America; common; parasitic.

4.Cap color orange-brown; stem dark and colored like the cap; growing on hardwoods (especially species of Alnus) in western North America.

Armillaria nabsnona
at Tom Volk's Fungi

4.Not as above.

5.Stem with a thick, membranous ring; stem bases pointed due to growth habit in dense clusters; basidia without basal clamps.

5.Ring ephemeral or cobwebby; stem bases not pointed; (at least some) basidia basally clamped.

6.Pathogenic and parasitic, invading the wood of hardwoods (in the northeast) and conifers (in the Pacific Northwest) with black rhizomorphs; mushrooms typically fruiting from visible wood.

Armillaria sinapina
At Tom Volk's Fungi

6.Harmlessly saprobic on hardwood (and occasionally conifer) roots east of the Rocky Mountains; not displaying prominent black rhizomorphs in the host wood; mushrooms often appearing terrestrial, though occasionally fruiting from visible wood.

7.Mating in the laboratory with previously identified isolates of Armillaria gallica; widely distributed east of the Rocky Mountains.

7.Mating in the laboratory with previously identified isolates of Armillaria calvescens; northeastern in distribution.
Armillaria calvescens
(see Armillaria gallica)


Anderson, J. B. & R. C. Ulrich (1979). Biological species of Armillaria mellea in North America. Mycologia 71: 402-412.

Anderson, J. B. (1986). Biological species of Armillaria in North America: Redesignation of groups IV and VIII and enumeration of voucher strains for other groups. Mycologia 78: 837-839.

Banik, M. T., J. A. Paul & H. H. Burdsall (1995). Identification of Armillaria species from Wisconsin and adjacent areas. Mycologia 87: 707-712.

Banik, M. T., T. J. Volk & H. H. Burdsall (1996). Armillaria species of the Olympic Peninsula of Washington state, including confirmation of North American biological species XI. Mycologia 88: 492-496.

Baumgartner, K. & Rizzo, D. M. (2001). Distribution of Armillaria species in California. Mycologia 93: 821-830.

Berube, J. A. & M. Dessureault (1988). Morphological characterization of Armillaria ostoyae and Armillaria sinapina sp. nov. Canadian Journal of Botany 66: 2027-2034.

Berube, J. A. & M. Dessureault (1989). Morphological studies of the Armillaria mellea complex: Two new species, A. gemina and A. calvescens. Mycologia 81: 216-225.

Brazee, N. J. & R. L. Wick (2011). Armillaria species distribution and site relationships in Pinus- and Tsuga-dominated forests in Massachusetts. Canadian Journal of Forestry Research 41: 1477-1490.

Brazee, N. J., B. Ortiz-Santana, M. T. Banik & D. L. Lindner (2012). Armillaria altimontana, a new species from the western interior of North America. Mycologia 104: 1200-1205.

Burdsall, H. H. & T. J. Volk (2008). Armillaria solidipes, an older name for the fungus called Armillaria ostoyae. North American Fungi 3: 261-267.

Coetzee, M. P. A. et al. (2000). Geographical diversity of Armillaria mellea s. s. based on phylogenetic analysis. Mycologia 92: 105-113.

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Hanna, J. W., N. B. Klopfenstein, M. -S. Kim, G. I. McDonald & J. A. Moore (2007). Phylogeographic patterns of Armillaria ostoyae in the western United States. Forest Pathology 37: 192-216.

Kelley, M. B., M. K. Fierke & F. M. Steohen (2009). Identification and distribution of Armillaria species associated with an oak decline event in the Arkansas Ozarks. Forest Pathology 39: 397-404.

Kim, M. -S., N. B. Klopfenstein, G. I. McDonald, K. Arumuganathan & A. K. Vidaver (2000). Characterization of North American Armillaria species by nuclear DNA content and RFLP analysis. Mycologia 92: 874-883.

Kim, M. -S., N. B. Klopfenstein, J. W. Hanna & G. I. McDonald (2006). Characterization of North American Armillaria species: genetic relationships determined by ribosomal DNA sequences and AFLP markers. Forest Pathology 36: 145-164.

Kim, M. -S. & N. B. Klopfenstein (2011). Molecular identification of Armillaria gallica from the Niobrara Valley Preserve in Nebraska. Journal of Phytopathology 159: 69-71.

Ross-Davis, A. L., J. W. Hanna, M. -S. Kim & N. B. Klopfenstein (2012). Advances toward DNA-based identification and phylogeny of North American Armillaria species using elongation factor-1 alpha gene. Mycoscience 53: 161-165.

Thiers, H. D. & Sundberg, W. J. (1976). Armillaria (Tricholomataceae, Agaricales) in the western United States including a new species from California. Madroño 23: 448-453.

Tsykun, T., D. Rigling & S. Prospero (2013). A new multilocus approach for a reliable DNA-based identification of Armillaria species. Mycologia 105: 1059-1076.

Vesterholt, J. (2008). Armillaria. In Knudsen, H. & J. Vesterholt, eds. Funga Nordica: Agaricoid, boletoid and cyphelloid genera. Copenhagen: Nordsvamp. 252-254.

Volk, T. J. & Burdsall, H. H. (1993). The state of taxonomy in the genus Armillaria. McIlvainea 11: 4-11.

Volk, T. J. and H. H. Burdsall, Jr. (1995). A nomenclatural study of Armillaria and Armillariella species. Synopsis Fungorum 8. Fungiflora: Oslo, Norway. 121 pp.

Volk, T. J., Burdsall, H. H. & Banik, M. T. (1996). Armillaria nabsnona, a new species from western North America. Mycologia 88: 484-491.

Volk, T. J. (2005). Key to North American Armillaria species. Retrieved May 18, 2017 from the Tom Volk's Fungi Web site:

Cite this page as:

Kuo, M. (2017, May). The genus Armillaria. Retrieved from the MushroomExpert.Com Web site: