The common occurrence of tri-membered symbiotic associations in the Peltigerinae offers a unique opportunity for studying coevolutionary trends among all symbionts involved in lichen symbioses. Based on a phylogenetic study of SSU and LSU nrDNA from the mycobiont and the cyanobiont found in a broad selection of species belonging to the Peltigerineae, a monophyletic circumscription of the suborder is proposed here. Ancestral symbiotic states (bi- versus tri-membered symbioses) for peltigerous lichens were reconstructed using maximum likelihood as the optimization criterion. In addition, the pattern of transmission (horizontal versus vertical) of cyanobacterial lineages during the evolutionary history of the Peltigerineae was investigated.

Key words: coevolution, cyanobacteria., lichen symbiosis, molecular phylogenetics, SSU &LSU nrDNA, symbiotic ancestral character states