Stigomena is a genus of cyanobacteria that is often the photobiont associated with the lichen genus Stereocaulon. To elucidate the evolutionary relationships between Stereocaulon and Stigonema and assess whether there is specificity or selectivity at the ecosystem or species levels, we performed phylogenetic analyses on specimens collected throughout Eastern Canada. We generated ITS sequences from the fungal component of the symbiosis and sequences from the operon rbcL-rbcX and the trnL ...