ABSTRACTCultures ofLeptosphaerulina crassiascafrom single ascospores formed ascostromata, indicating that the fungus is homothallic. Mycelial hyphae were septate, with uninucleate cells, and they gave rise to fertile hyphae which were larger and had binucleate or multinucleate cells. Certain cells of the fertile hyphae divided repeatedly in all planes to form ascostromal initials. Small binucleate ascogonial cells with dense cytoplasm soon filled the central part of the young ascostroma; later they give rise to ascogenous cells that developed directly into asci. No sterile centrum tissues were formed. The asci contained eight ascospores which were initially uninucleate. Mature ascospores were multinucleate and had 3–5 transverse septa and 0–2 longitudinal septa. The ascus wall was two-layered, with the inner layer (endotunica) extending through the outer layer (ectotunica) during ascospore discharge. The ascoma is a uniloculate pseudothecium with a papillate ostiolar neck and bitunicate asci. Ascomal ontogeny is typical of theDothideatype of development.