Armillaria mellea is a basidiomycete that is known as both a plant pathogen and as an edible, with the common name ‘honey mushroom.’
A. mellea produces honey colored mushrooms with an annulus near the base of the cap. The caps often are darker in the middle and fade out into a more classic honey color along the margins. The mushrooms grow in clusters and caps can get up to six inches in diameter (Figure 1).
Another interesting feature of this fungus is the fact that it produces rhizomorphs (Figure 2). Rhizomorphs are dark, thick hyphae structures that allow Armillaria to move quicker. If one suspected that their hardwood tree was dying due to a root rot, one way to determine if it is Armillaria is to pull back the bark and check for the next of rhizomorphs moving up the tree. The rhizomorphs isolated in figure 2 were collected this way.
The last sign of this fungus attacking a tree is a white mycelial fan that occurred under the bark of an infected tree as well.
The tail-tell sign of separating A. mellea from other Armillaria species is their basida are not clamped at the bases.
Figure 1: Close up of immature A. mellea mushrooms near base of a dead oak tree in Baker’s wood lot on Michigan State University’s campus.
Figure 2: Collection made from dead oak tree in Baker’s wood lot on MSU campus. There were three stages of A mellea present on oak stump; top of picture are rhizomorphs, bottom left are young mushrooms; bottom right are mature mushrooms.
Figure 3: Pure culture of A. mellea grown from a single spore obtained from a mature mushroom. Note the rhizomorphs growing through the agar.
Armillaria mellea is considered a northern hemisphere fungi, occurring in northern North America, Europe and Asia (McKnight and McKnight, 1987).
Armillaria mellea is a common problem in hardwood plantings in Michigan. A large concern of this pathogen comes from sour cherry growers, who can lose large swaths of orchards to this disease (Proffer et al., 1987). The rhizomorphs can move down a row of cherries rather quickly. Horticulturists have also attempted to breed resistant cherry rootstock, with little success.
Armillaria mellea is edible, but it is not everyone’s favorite foraged mushroom. They can range from a ‘mild mushroomy’ taste to a more ‘bitter mushroomy’ taste that gets sweeter as the meal goes on (personal observation). They are good in stir frys and just fried up with oil; I personally like them when they are young and more ‘button’ shaped (like in Figure 2, bottom left).
As always, if you are not sure about the identification of a mushroom, do not eat it. There are plenty of other mushrooms that resemble Armillaria spp one being a jack-o-lantern fungus.(http://www.mushroomexpert.com/omphalotus_illudens.html)
Proffer, T. J., Jones, A. L., and Ehret, G. R. 1987. Biological species of Armillaria isolated from sour cherry orchards in Michigan. Phytopathology 77:941-943.
McKnight, K. H., & McKnight, V. B. (1987). Mushrooms of North America. Norwalk, CT: Easton Press. Page 136: Armillaria mellea.11.27.16