Aleurodiscus wakefieldiae

Scientific name: Aleurodiscus wakefieldiae Boidin &
Beller  
Derivation of name: Wakefieldiae refers to Dr. Elsie
Wakefield, a mycologist at the Royal Botanic Gardens.
Synonyms: Aleurodiscus oakesii (Berkeley & Curtis)
Hoehnel & Litschauer, Corticium oakesii Berk. & M.A.
Curtis 
Common name(s): Hop hornbeam disc.  
Phylum:   Basidiomycota
Order:   Russulales
Family:   Stereaceae
Occurrence on wood substrate: Saprobic; scattered to
clustered on bark of living hardwood trees, particularly
oak; year round.   
Dimensions: Flattened disc or cup-shaped fruit bodies 1-
10 mm in diameter, shape irregular at times, sometimes
confluent with other fruit bodies to form larger structures.    
Description: The tough, leathery fruit bodies are attached
at a single point. The margin is free and often elevated
giving the structure the appearence of an ascomycete cup
fungus. The smooth, fertile center area of the disc is tan to
brownish-pink to pale brown. The outer sterile portion is
whitish and cottony.         
Edibility: Inedible.  
Comments:  The effect of this fungus on the bark of a tree
is more readily observed than is the fungus itself.
Aleurodiscus wakefieldiae causes a disorder referred to
as "white bark disease" or "smooth patch disease" because
of the manner in which it digests the outer bark of the tree.
As the deeply furrowed outer bark is digested, large areas
of the bark appear smoother and lighter in color as in
Figures 1-3. The fungus is not considered a parasite,
however, because it feeds on dead outer bark cells and
not living tissue.

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Figure 1. The smooth areas of bark on this living white
oak (Quercus alba) are evident at a distance.
Photo © Gary Emberger.

Figure 2. Closer view of the tree in Figure 1. The lighter
color of the smooth areas is due, in part, to the lack of
deep furrows. Photo © Gary Emberger. 

Figure 3. Same tree as in Figures 1 and 2. The smooth bark
may completely surround the tree. Photo © Gary Emberger.

Figure 4. The interface of normal and affected bark. The
pale brownish fruit bodies of Aleurodiscus wakefieldiae
are visible on the colonized lower portion of the bark.
Photo © Gary Emberger.

Figure 5. Fruit body shapes range from circular to irregular.
Photo © Gary Emberger.

Figure 6. Although attached at a central point, the margin is
free and often elevated. As a result, these basidiomycete
fruit bodies may be mistaken for an ascomycete cup fungus.
Note the whitish, fuzzy or cottony underside (raised edge).
Photo © Gary Emberger.

Figure 7. Fruit bodies of Aleurodiscus wakefieldiae often
merge together forming larger structures.
Photo © Gary Emberger.