Ascomata subcuticular. In vertical section upper wall of unopened ascomata up to 100 µm thick. Outer part of wall comprising dense, black material, in a layer up to 50 µm wide toward the centre of the ascomata, with the inner part comprising brown to pale brown, thin-walled, angular cells. In a narrow line, along the future line of opening, the paler cells extend almost to the outside of the wall. A few hyaline, thin-walled, cylindric cells line the inside of the wall. In opened ascomata the upper wall is up to 110 µm thick near the opening, becoming thinner toward the base, the outer part and the part of the wall near the ascomatal opening comprising dense, black tissue with no visible cellular structure; the inner part of pale, thin-walled, angular cells. The exposed face of the broken wall becomes lined with a layer of cylindric, hyaline to brown, thin-walled, 15-20 x 3-4 µm cells. Lower wall less than 5 µm thick, of one layer of dark brown, angular, thick-walled cells.

Paraphyses 1-2 µm diam., undifferentiated at apex, barely extending beyond asci. Asci 120-160 x 17-22 µm, clavate, becoming clavate-stipitate prior to spore release, tapering to truncate apex, wall slightly thinner across apical part of ascus, 8-spored. Ascospores 24-39 x 3.5-5 µm (average 33.4 x 4.1 µm) bifusiform, 1.5-2.0 µm wide at central constriction, 1-septate, surrounded by gelatinous sheath. Ascospores within the ascus often breaking across the central septum into two part-spores. When this occurs ascoconidia are produced from the broken end of each part-spore, and the asci eventually become full of the 4.0-7.5 x 1.0-1.5 µm, cylindric, 0-septate, hyaline ascoconidia.

Conidiomata subcuticular. In vertical section lenticular in shape. Upper wall 5-10 µm thick, comprising dark brown tissue with noo bvious cellular structure. Lower wall 5-15 µm thick, of 1-3 rows of dark brown, thick-walled, angular cells. Conidiogenous layer develops on lower wall. Conidiogenous cells 8-13 x 1.5-2.5 µm, cylindric, tapering near apex, wall slightly thickened at the single, apical conidiogenous locus, proliferation percurrent. Conidia 3.5-4.5 x 1.0-1.5 µm, oblong-elliptic, 0-septate, hyaline.

ETYMOLOGY: named after host substrate.

NOTES: This is the only Hypoderma species in New Zealand known from a fern. It is easily distinguished from other species by its large ascomata, black-walled conidiomata, large asci, and by its 1-septate, often disarticulating ascospores. The appearance of the upper wall of unopened ascomata is distinctive with its broad inner layer of pale, thin-walled cells.