Ascomata subcuticular. In vertical section the upper wall of unopened ascomata is up to 50 µm thick, becoming gradually narrower toward the edge of the ascomata, comprising mostly brown to dark brown, angular cells, but along the future line of opening, near the middle of the ascomata, is a wedge-shaped group of paler, thinner-walled cells in the inner part of the wall. The inside edge of the wall is lined with a few hyaline, cylindric to globose cells. In opened ascomata the upper wall is 40-55 µm thick, not varying in width in the top third of the wall, in the lower two-thirds becoming gradually thinner. Wall comprising dark brown, mostly thick-walled, angular, 5-8 µm diam. cells. Exposed face of the broken upper wall is lined with hyaline, thin-walled, 15-20 x 3-4 µm, cylindric cells. Lower wall, 10-1 5 µm thick, of 3-4 layers of dark brown, thick-walled, globose to angular cells.

Paraphyses 1-1.5 µm diam., undifferentiated or loosely circinate at apices, extending 10-15 µm beyond asci. Asci 120-155 x 8-12 µm, clavate-stipitate, tapering to small, truncate apex, wall undifferentiated at apex, 8-spored, spores confined to upper half of ascus. Ascospores 21-29 x 2-3 µm (average 23.2 x 2.7 µm), in face view more or less cylindric, tapering from near the base toward the acute base, 0-septate surrounded by narrow gelatinous sheath.

Conidiomata subcuticular. In vertical section upper wall 5-10 µm thick, comprising dark brown material with no visible cellular structure. Lower wall of 1-3 layers of brown to dark brown, thick-walled, angular cells. Lower wall lined with 1-2 rows of hyaline, thin-walled cells on which the conidiogenous cells develop. Conidiogenous cells 10-15 x 1.5-2.0 µm, cylindric, tapering toward apex, with both sympodial and percurrent proliferation, no obvious thickening of wall at conidiogenous loci. Conidia 3-4.5 µm, straight, cylindric, ends rounded, hyaline.

ETYMOLOGY: named after type locality.

NOTES: Hypoderma dundasicum is very similar to the widespread H. rubi. The two species can be distinguished by ascospore size and shape, and ascus width. The appearance of the ascomatal wall in vertical section also differs, with the wall of H. rubi decreasing in width from the edge of the opening, while in H. dundasicum the uppermost part of the wall is more or less uniform in width. H. rubi has not been found on Ericaceae in New Zealand, although Powell (1974) reported it on ericaceous hosts from the northern hemisphere. H. gaultheriae Hunt, described on Gaultheria from North America by Hunt(1980) is reported to be associated with necrotic spots on green leaves, and has ascospores wider than those of H. dundasicum.