Molecular phylogenetic analyses based on the complete plastid genomes and nuclear sequences reveal Daphne (Thymelaeaceae) to be non-monophyletic as current circumscription

Abstract

The diverse members of the genus Daphne are prized for their fragrant flowers. Despite being promising ornamental plants in many countries, genetic information of Daphne is scarce. In this study, the plastomes of four species and one variety of Daphne were sequenced and analyzed. The plastomes were typical and contained a pair of inverted repeat (IR) regions that separated the large single-copy (LSC) region from the small single-copy (SSC) region. With a length ranging from 132,869 bp (D. genkwa) to 174,773 bp (D. championii), 106 to 141 genes were predicted. Comparative plastome analysis of the newly sequenced plastomes with four publicly available Daphne plastomes identified an expansion of the IRs, sequence variations, and mutational hotspots. Phylogenetic analyses indicated that the genus Daphne in its current circumscription is polyphyletic. Daphne genkwa was nested within the genus Wikstroemia, while D. championii was well resolved as sister to Edgeworthia. These findings concurred with results from our study that used nuclear ribosomal internal transcribed spacer sequence data. The conflicts on the molecular placement of D. championii and D. genkwa and the present taxonomic classification in Daphne suggest that a new intergeneric classification system of Daphneae warrants consideration.