FIG. 4.
Phylogenetic tree including all published tRNALeu intron sequences from cyanobacteria of the order Nostocales (section IV). Only the conserved, readily alignable parts of the intron have been used in this analysis (for details, see the text). Bootstrap values are shown above branches, and jackknife fractions are shown under branches. The intron sequences of all examined lichen cyanobionts are grouped with the sequences of the free-living Nostoc strains also used in this study. In the phylogenetic analysis, only few characters are informative within this group (Fig. 3c). The additional information present in the variable parts of the intron is difficult to use in this kind of phylogenetic analysis because they are not readily alignable, but it can be of great value when analyzing closely related cyanobacteria such as the lichen cyanobionts.