AbstractWe studied ascospore dispersal and ontogeny in several species ofTrypetheliaceaeand one species ofGraphidaceaewith megalosporous (very large) ascospores, includingAptrootia terricola(Aptroot) Lücking, Umaña & Chaves,Architrypethelium nitens(Fée) Aptroot,A. seminudum(Mont.) Aptroot,Astrothelium diplocarpoidesMüll. Arg.,Laurera gigantospora(Müll. Arg.) Zahlbr., andOcellularia subpraestansHale. Although mature ascospores are very different among species ofTrypetheliaceae, all species studied share plesiomorphic ontogenetic features such as the formation of a single central euseptum and subsequent development of a variable number of transverse distosepta with diamond-shaped lumina (astrothelioid ascospore type). Even the dark brown, richly muriform ascospores ofAptrootia terricolago through an astrothelioid stage. This suggests that ascospore types may be more closely related than suggested by their mature morphology, and could explain why related taxa can develop markedly different ascospore types. We discuss the implications for systematic classification ofTrypetheliaceaein the light of recent molecular studies, and also speculate about the ecological importance of large ascospores, especially with muriform septation.