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Armillaria mellea: The Honey Mushroom
by Michael Kuo
In the good-old days, not so long ago, there were two North American "honey mushrooms": Armillaria mellea and Armillaria tabsescens--and the genus Armillaria held many mushrooms, including the matsutake mushroom, which was known as "Armillaria ponderosa."
This state of affairs was too easy for mycologists, however. Someone had to go and point out that Armillaria contained many mushrooms that differed widely in their physical features. More importantly, mycologists pointed out that the mushrooms in question differed in their fundamental ecological roles. Most of the honey mushrooms, for example, were parasitic wood rotters (often pathogenic and killing the tree), while the matsutake was mycorrhizal.
For a while mycologists played around with the idea of putting the honey mushrooms into a separate genus called "Armillariella," but eventually it became clear that most of the 250 or so species of Armillaria (not just the "honeys") needed to be distributed among other genera. The matsutake became Tricholoma magnivelare. Things snow-balled, and in the "end" Armillaria was a very small genus containing only a few species, most of which colonized wood with black, stringy rhizomorphs.
Still not satisfied, mycologists had to go and "mate" the remaining Armillaria species in petri dishes. They discovered that some honey mushrooms would take to one another, while others turned up their fungal noses at the idea of pairing up. Thus, using the "biological species concept" (the concept we usually use, for example, to define species of large animals; if they can't mate they belong to separate species), these mycologists defined about nine or ten species of Armillaria in North America. All well and good, except that some of these species don't look different, and must be "mated" to be identified with certainty. Fortunately, physical features do separate some of the species, and the fairly well documented geographical ranges of the mushrooms help to separate others (though some pairs of species, like Armillaria gallica and Armillaria calvescens, remain basically inseparable if the mushrooms are found in certain geographical areas).
The classic honey mushroom, Armillaria mellea, turns out to be limited to roughly the eastern half of North America, from about the Great Lakes to the Gulf Coast and the East Coast--and perhaps to northern California, where it has been reported. It usually grows in clusters on hardwoods, but is occasionally found on conifers. It has a fairly smooth cap, a sturdy ring on the stem, and fused stem bases that are tapered to points. Under the microscope, it has basidia that are not clamped at their bases.
Be sure to check out Entoloma abortivum to see what happens when the honey mushroom is attacked by another mushroom!
Ecology: Pathogenic and parasitic on the wood of hardwoods (and occasionally on conifers); causing a white, pulpy rot in the wood; spreading through wood, and from tree to tree, by means of long black rhizomorphs; mushrooms typically appearing in large clusters on wood in the fall after rains, but found nearly year-round in warmer climates; eastern and southeastern North America.
Cap: 3-15 cm, convex to broadly convex or flat in age; the margin often arched in maturity; dry or tacky; color extremely variable, but typically honey yellow; smooth, or with a few tiny, dark scales concentrated near the center and vaguely radially arranged.
Gills: Attached or beginning to run down the stem; nearly distant; whitish, sometimes bruising or discoloring darker.
Stem: 5-20 cm long; .5-3.5 cm thick; tapering to base due to clustered growth pattern; tough and fibrous; smooth and pale near apex, darker and nearly hairy below; with a persistent ring at maturity and a white partial veil covering the gills when young.
Flesh: Whitish to watery tan.
Odor and Taste: Taste mild to bitter; odor sweet.
Spore Print: White.
Microscopic Features: Spores 7-9 x 6-7 µ; smooth; more or less elliptical; inamyloid; with a prominent apiculus. Basidia lacking basal clamps.
Armillariella mellea is a synonym.
REFERENCES: (Vahl, 1790) Kummer, 1871. (NOTE: Field guide references before 2000 predate the contemporary, limited concept of Armillaria mellea. Saccardo, 1887; Kauffman, 1918; Smith, 1949; Smith, 1975; Smith, Smith & Weber, 1979; Weber & Smith, 1985; Arora, 1986; Berube & Dessureault, 1988; Berube & Dessureault, 1989; States, 1990; Phillips, 1991/2005; Lincoff, 1992; Metzler & Metzler, 1992; Horn, Kay & Abel, 1993; Barron, 1999; Roody, 2003; Volk, 2003; McNeil, 2006; Miller & Miller, 2006; Kuo, 2007.) Herb. Kuo 09200101, 09230608, 05210701.
Further Online Information:
Armillaria mellea at Tom Volk's Fungi
The pages linked below represent "Armillaria mellea" in its former, broad sense--and may or may not correspond with the current species definition.
Above: Not the most attractive photo, but it has the advantage of representing mushrooms that were held up to Armillaria expert Tom Volk with the query: "Which one?" Volk, without hesitation, replied, "That's mellea." (The crowd went wild.)
Cite this page as:
Kuo, M. (2004, October). Armillaria mellea. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/armillaria_mellea.html