Ascomata in vertical section with an upper wall 80-100 µm thick near the base, increasing to 300-500 µm thick near the ascomatal opening, comprising mostly brown to pale brown, slightly thick-walled, angular, 5-10 µm diam. cells, but the cells along the outer edge of the wall darker and thicker walled. The part of the wall adjacent to the ascomatal opening lined with a 30-65 µm wide, palisade-like layer of 35 µm diam., cylindric, thin-walled, hyaline cells. Lower wall 30-65 µm thick, comprising dark brown, thick-walled, 4-8 µm diam., angular cells, the outer rows of cells darker and thicker walled than the inner rows. A 10-20 µm wide layer of thin-walled, hyaline, cylindric cells separates the hymenium from the lower wall.

Paraphyses with anastomoses near bases, 1-2 µm diam., undifferentiated or irregularly circinate at the apex, extending up to 10 µm beyond the asci. Asci 210-330 x (18-)20-26 µm, clavate-stipitate, tapering to truncate apex, wall unthickened at apex, but often with small apical pore, nonamyloid, 8-spored, spores confined to upper 90-150 µm of ascus, ascus development sequential. Ascospores (26-)31-46 x 6-10 µm, oblong-elliptic, 0-3 septate, hyaline, surrounded by a 1-2 µm thick gelatinous sheath.

ETYMOLOGY: refers to host substrate.

NOTES: C. nothofagi, with phragmosporous ascospores, keys out to the genus Xyloschizon in Darker's (1967) key to the Rhytismataceae. However, Darker (p. 1415) noted that Xyloschizon appears to be segregated from Colpoma simply on the basis of ascospore septation, and as such is of doubtful validity. I do not consider ascospore septation a useful character at the generic level in the Rhytismataceae.