The Lichenologist

Research Article

Ascospore ontogeny and discharge in megalosporous Trypetheliaceae and Graphidaceae (Ascomycota: Dothideomycetes and Lecanoromycetes) suggest phylogenetic relationships and ecological constraints

Garrett SWEETWOODa1a2, Robert LÜCKINGa2, Matthew P. NELSENa2a3 and André APTROOTa4

a1 Roosevelt University, 430 S. Michigan Ave, Chicago, Illinois 60605, USA.

a2 Department of Botany, The Field Museum, 1400 South Lake Shore Drive, Chicago, Illinois 60605-2496, USA. Email:

a3 Committee on Evolutionary Biology, University of Chicago, 1025 E. 57th Street, Chicago, Illinois 60637, USA.

a4 ABL Herbarium, G.v.d.Veenstraat 107, NL-3762 XK Soest, The Netherlands.


We studied ascospore dispersal and ontogeny in several species of Trypetheliaceae and one species of Graphidaceae with megalosporous (very large) ascospores, including Aptrootia terricola (Aptroot) Lücking, Umaña & Chaves, Architrypethelium nitens (Fée) Aptroot, A. seminudum (Mont.) Aptroot, Astrothelium diplocarpoides Müll. Arg., Laurera gigantospora (Müll. Arg.) Zahlbr., and Ocellularia subpraestans Hale. Although mature ascospores are very different among species of Trypetheliaceae, 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 of Aptrootia terricola go 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 of Trypetheliaceae in the light of recent molecular studies, and also speculate about the ecological importance of large ascospores, especially with muriform septation.

(Accepted September 22 2011)