SMALL INSERTIONS AT A SHARED POSITION IN THE SSU RDNA OF LECANORALES (LICHEN-FORMING ASCOMYCETES)

Small insertions are reported from the SSU rDNA of the genera Cladonia , Cladina, Stereocaulon, Pertusaria and Physcia (lichen-forming Lecano rales, Ascomycetes). The insertions range in length from 56 to 81 nucl eotides, and occur at a shared position, 330 (relative to Escherichia coli), in a semi-conserved region of the SSU rDNA. These small inserti ons have a simple secondary structure with two stem-loops, and may rep resent degenerate group-I introns. Species of the same genus often hav e small insertions of similar lengths, secondary structures and sequen ces. These similarities suggest that the insertions are homologous and can provide phylogenetic information to support current classificatio ns. Variable sequences of rDNA, such as the small insertions and group -I introns, may be powerful tools for resolving evolutionary relations hips among genera and species.