Ascocarps in vertical section subcuticular. Upper wall 10-15 µm wide near outside edge of ascocarp, up to 100 µm wide near ascocarp opening, comprising dark brown, thick-walled, 4-7 µm diam. cells. Layer of cylindric, hyaline, thin-walled, 20-45 x 3-4 µm cells developing across exposed face of broken upper wall. Lower wall 10-15 µm wide, of 3-4 rows of brown to pale brown cells.

Paraphyses 1-1.5 µm diam., circinate at apex. Asci 170-195 x 9-10.5 µm, subclavate, tapering to small, truncate apex, wall not thickened, 8-spored, spores in upper part of ascus only. Ascospores 80-105 x 2-2.5 µm, 0-1 septate, with narrow gelatinous sheath.

Pycnidia-like structures subcuticular. No conidiogenous cells or conidia seen.

ETYMOLOGY: croesicum; refers to type locality.

In vertical section L. croesicum is indistinguishable from L. atrum and L. cf. richeae. The three species differ in the macroscopic appearance of both ascocarps and pycnidia, in the size of asci and ascospores, and in host substrate. None of the subcuticular Lophodermium spp. considered by Tehon (1935)(as Lophodermina Höhnel) match any of the New Zealand species.