Apiosporina morbosa

Scientific name:  Apiosporina morbosa (Schwein.) Arx
Derivation of name:  Morb- means "disease" and is a fitting
epithet for this parasitic fungus.
Synonyms: Sphaeria morbosa Schwein. 
Common name(s):  Black knot of cherry, poop on a stick.
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.      
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).
Photo © Gary Emberger.
    

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

Figure 3. This growth has completely encircled the twig.
Photo © Gary Emberger.

Figure 4. The growths are quite irregular, bumpy, and
fissured. Photo © Gary Emberger.

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