Ascocarps in vertical section subcuticular, upper wall 10-15 µm wide near edge of ascocarp, 50-60 µm wide near ascocarp opening, comprising mostly very dark tissue with no obvious cellular structure. A poorly developed layer of hyaline, cylindric, 10-15 x 1.5-2.5 µm cells forms across the exposed face of the broken upper wall. Lower wall 15-40 µm wide, of dark brown, thick-walled cells.

Paraphyses 2-2.5 µm diam., gradually increasing in width to 3-4.5 µm diam. at apex, embedded in gel, extending 10-20 µm beyond asci. Asci 85-115 x 7-9 µm, cylindric, tapering to small, rounded apex, wall not thickened at apex, 8-spored. Ascospores 55-80 x 1.5-2 µm, 0 septate, poorly developed gelatinous sheath.

Pycnidia in vertical section subcuticular, lenticular in shape, upper wall 3-5 µm wide, comprising black tissue with no obvious cellular structure. Lower wall 8-12 µm wide, of dark brown, thick-walled cells, with a column of hyaline, filiform elements near centre of pycnidium extending almost to upper wall. Conidiogenous cells lining lower wall, solitary, cylindric to flask-shaped, sympodial. Conidia 4.5-6 x 0.8 µm, cylindric, hyaline, 0 septate.

ETYMOLOGY: rectangulare = rectangular; refers to shape of ascocarp.

NOTES: Ascocarp and ascocarp opening are macroscopically distinct. Although species included in Lophodermium typically do not have a branching ascocarp opening, to exclude L. rectangulare from Lophodermium for this reason alone would be misguided.