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: There are a number of other blackish,
crust-like species which can be mistaken for Diatrype
stigma. One 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.


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 presence of flat, black discs covering the stromatal
surface. The dimpled area in the center of each disc is a
perithecial ostiole. The stromatal tissue between the discs is
brown/reddish-brown. Diatrype stigma, in contrast, lacks discs,
has more pointed perithecial ostioles, and the stromatal tissue
surrounding the perithecia is blackish.
Photo © Ethan Crenson.