High diversity of Bacidia (Ramalinaceae, Lecanorales) species in the Caucasus as revealed by molecular and morphological analyses

During a study of the incompletely known lichen flora of the Caucasus, we analyzed 237 specimens of corticolous Bacidia s. str. collected in the Northern and Southern Caucasus, including Armenia, Azerbaijan, Georgia, and Russia. Of these, 54 specimens belonging to 11 species of Bacidia s. str. were selected for molecular studies, representing the observed morphological variability of the genus. We obtained 142 sequences from three RNA-coding genes (nrITS, nrLSU, and mtSSU) and two protein-coding genes (RPB1 and RPB2). The single and concatenated datasets were complemented with Bacidia s. str. sequences from GenBank and subjected to Bayesian inference and two maximum likelihood analyses (RAxML and IQ-TREE). The resulting trees yielded highly concordant topologies of the groups and corresponded with previous results, supporting two main clades correlating with apothecia pigmentation. Our analyses are the first to reveal the presence of Bacidia heterochroa in the Caucasus. An exceptionally high degree of morphological plasticity was found in the Rubella and Suffusa groups. As a result of morphological examination and phylogenetic results, B. caucasica (Suffusa group) was described as new to science. Furthermore, two putative taxa in the Rubella group, Bacidia inconspicua ined. and B. maritima ined., were introduced. This study furthers our understanding and documentation of the understudied lichen flora of the Caucasus, bringing the total number of Bacidia species for the region to 13.