Apiosporina morbosa

Scientific name:  Apiosporina morbosa (Schweinitz) van Arx
Derivation of name:  Morb- means "disease" and is a fitting
epithet for this parasitic fungus.
Synonyms:  
Common name(s):  Black knot of cherry.
Phylum:   Ascomycota
Order:   Pleosporales
Family:   Venturiaceae
Occurrence on wood substrate:  Parasitic; solitary to several,
forming growths on branches and twigs of cherry and plum
trees; found year-round.  
Dimensions: Fruitbody 3.5 to 14 cm long and 1 to 2.5 cm
thick.   
Description:  These black, hard, furrowed and cracked
ascocarps form irregular elongated swellings which clasp and
surround twigs of cherry and plum. Perithecia are embedded
just below the surface.      
Edibility: Inedible.   
Comments: This fungus is a widespread and destructive
pathogen of cherry trees.

More information at MushroomExpert.com:  


Figure 1. Appearance of black knot on branches of wild black
cherry (Prunus serotina).
    

Figure 2. The black, carbonaceous growths of Apiosporina
morbosa can be quite extensive on a twig. Note that the twig
still supports living leaves.

Figure 3. This growth has completely encircled the twig.

Figure 4. The growths are quite irregular, bumpy, and
fissured.

Figure 5. Beneath the minutely bumpy surface is a layer of
perithecia containing asci with ascospores.