Diatrype stigma

Scientific name:  Diatrype stigma (Hoffm.) Fr.
Derivation of name:  Stigma means "a spot" perhaps in
reference to the tiny "spotlike" bumps of the perithecia on the
surface of the crust.
Synonyms: Sphaeria stigma Hoffm. 
Common name(s): Common tarcrust (British name) 
Phylum:   Ascomycota
Order:   Xylariales
Family:   Diatrypaceae
Occurrence on wood substrate: Saprobic; forming
sheet-like growths (stromata) on decaying hardwood
branches, particularly beech; year-round.   
Dimensions:  The black crusts (stromata) of this fungus
vary from a few mm to more than 10 x 20 cm in size and
0.2-0.7 mm thick.  
Description: The blackish-brown to black surface is shiny,
finely roughened to smooth, and sometimes minutely cracked.
The ostioles (i.e., openings) of the perithecia project
slightly from the stromatal surface, forming tiny bumps
marking the locations of perithecia embedded just below
the surface in a single layer. Flesh whitish.      
Edibility: Inedible.  
Comments: A blackish, crust-like species which can
be mistaken for Diatrype stigma is Graphostroma
platystomum, pictured in Figures 3 and 4. The
two species differ macroscopically but with age, the
differences may become obscure and microscopic
examination may be required. Graphostroma
platystomum causes problems when it grows on the
bed logs used for cultivation of Lentinula edodes, the
shiitake mushroom.


Figure 1. An old specimen of Diatrype stigma. This is a
common fungus on beech branches where the fungus often
encircles the branch. The fungus gives the impression that
the wood is burned. Cracks are common in older specimens.
Photo © Gary Emberger.

Figure 2. When magnified with a hand lens, the tiny
bumplike pores of the embedded perithecia can be
seen all over the stromatal surface of the fungus.
Photo © Gary Emberger.

Figure 3. The look-alike species Graphostroma platystomum
on spice bush (Lindera benzoin). This specimen was photographed
in December at Inwood Hill Park in Manhatten, NYC. This
saprobic fungus is reported to occur on a number of hardwoods
including maple and oak. From a distance, the species is blackish
like Diatrype stigma and, like D. stigma, may develop cracks with
age. The species is described as indefinitely effused, varying from
5x5 mm to more than 20x20 cm in size and 0.3 to 1.5 mm thick.
Photo © Ethan Crenson.

Figure 4. This magnified image of Graphostroma platystomum
reveals the perithecia ostioles to be flat, blackish, and disc-shaped.
The surrounding stromatal tissue is brown/reddish-brown. In
contrast, the ostioles of Diatrype stigma are not flat and
disc-shaped and the stromatal tissue surrounding the perithecia
is blackish.
Photo © Ethan Crenson.