A new genus, Caucasoseris, is established to accommodate Prenanthes abietina, a species of hitherto uncertain systematic position distributed in the western Caucasus and northeasternmost Turkey in montane conifer and mixed forests. Agreement has existed that the species belongs somewhere in the Crepidinae or Lactucinae but its morphological features do not match any genus and previous molecular phylogenetic analyses could not establish its sister group. This study provides additional micro- and macromorphological, palynological and anatomical data, and used a molecular phylogenetic sampling designed to ascertain its relationship. A sister group relationship with the Chondrillinae is inferred from the phylogenetic tree based on nrITS. In the plastid DNA tree, where the Chondrillinae are resolved as a clade nested inside the Crepidinae, the species is resolved further remote from the Chondrillinae clade and in a rather early diverging position of the Crepidinae. In agreement also with the anatomical and micro- and macromorphological findings, it is considered an orphan lineage with affinities to the Chondrillinae, best treated as a genus of its own. A key to the genera of the Chondrillinae including Caucasoseris is provided.
