Summary:
Features include 1) erumpent growth on aspen and sometimes other hardwoods, 2) cankers that are crusty, cracked, and white-pruinose then black, the cankers having gray perithecia and gray dusty conidial pegs between bark and cambium, 3) not exuding pigments when a small piece is placed in 10% KOH on a microscope slide, 4) a germ slit on the concave side of the spore, and immature spores bearing a cellular appendage, and 5) the ascus tip containing an amyloid plug clearly visible at 400x. In eastern North America, "Hypoxylon canker is a very important and damaging disease of aspen, especially in stands predisposed by weather or insect damage", but in BC it is infrequently collected and has not been associated with heavy damage within stands, (Callan).

Microscopic:
SPORES 20-33 x 9-12 microns, oblong-elliptic with obtuse ends, dark brown, uniseriate or obliquely uniseriate; ASCUS 140-200 x 12-16 microns in spore-bearing part, cylindric, with stem 30-40 microns long; PARAPHYSES present; PERITHECIUM 700-1000 microns in diameter, spherical to ovate, (Miller, J.H.), SPORES 20-33 x 9-12 microns, elliptic, with one side flattened, blackish brown, with straight germ slit appearing under high magnification as a pale line on the concave side of the spore; ASCUS 8-spored, cylindric, long-stemmed, with prominent rectangular plug that turns blue in Melzer''s reagent; CONIDIUM 5.5-8.0 x 1.5-4.0 microns, single-celled, colorless, (Callan)

Notes:
Entoleuca mammata has been found in BC, WA, ON, NF, AK, CO, IA, MA, ME, MI, MN, MO, ND, NH, NJ, NY, PA, VA, WI, WY, Finland, Germany, and Sweden, (Miller, J.H.).