Circumscription of Primula subgenus Auganthus (Primulaceae) based on chloroplast DNA sequences

Recent molecular phylogenetic analyses of Primula have greatly enhanced our understanding of the infrageneric relationships of the genus, but the subgenera Auganthus and Carolinella remain meagerly sampled and poorly understood. In the present study, nucleotide sequence data of three chloroplast DNA regions (matK, rps16, and trnL-F) were used to infer phylogenetic relationships of the subgenera Auganthus and Carolinella. Sequence data were acquired and analyzed for 70 species of Primula and its close relatives. The data matrix included 29 species (42%) of subgenus Auganthus and five species (50%) from subgenus Caroline/la. Phylogenetic analyses on these data showed that the sampled species of the subgenus Carolinella do not form a monophyletic clade, but are dispersed among the species of the subgenus Auganthus. Therefore, neither subgenus Auganthus nor Carolinella is monophyletic under their current circumscriptions. The distinctive calyptrate capsule that was previously used as a diagnostic criterion for subgenus Caroline/la was inferred to have evolved multiple times in Primula based on the phylogeny. Our analysis also confirmed that Cortusa is nested within subgenus Auganthus. We therefore suggest a revised circumscription of subgenus Auganthus to include subgenus Caroline/la and the genus Cortusa. Several clades were identified with this broadly defined subgenus Auganthus by the phylogenetic analyses, but their relationships remain incompletely resolved.