Lichenizing Rhizomorphs and Thallus Development in the Squamulose Lichen Aspicilia crespiana Rico ined . (Lecanorales, Ascomycetes)

This work describes the rhizomorphs and their relation to thallus development in the squamulose lichen Aspicilia crespiana Rico ined. The rhizomorphs capture algal cells, giving rise to new squamules terminally or laterally. The thallus thus consists of a network of lichenized squamules interlinked by mycobiontic rhizomorphs. A previously proposed comparison of lichen rhizomorphs to the prothallus (hypothallus) of crustose lichens is applied and expanded upon. Other less organized prothallic structures sometimes produced by A. crespiana are also described. The importance of lichenizing rhizomorphs as an essential feature of thallus growth in this species is emphasized and a competitive role in substrate occupation and thallus expansion is suggested.