Eun Su Kang1P, Hye Been Kim1, Ju Eun Jang1, Dong Chan Son1

1Division of Forest Biodiversity, Korea National Arboretum, Pocheon, Korea

Richardia brasiliensis, an alien plant discovered in Jeju, belongs to the tribe Spermacoceae, where commonly used chloroplast regions for phylogenetic analyses (e.g., rbcL and atpB) are relatively conserved, limiting phylogenetic resolution and motivating efforts to identify more variable chloroplast regions. Here, we sequenced and annotated the complete chloroplast genome of R. brasiliensis and conducted a basic phylogenetic analysis and a preliminary comparative analysis using the genome of related taxa. The chloroplast genome is 154,573 bp (LSC 84,388 bp; SSC 17,411 bp; IRs 26,387 bp each) with a GC content of 43% and contains 127 genes (82 CDSs, 37 tRNAs, and 8 rRNAs); atpF is intronless and infA is a pseudogene. Phylogenetic inference based on 77 CDSs indicated that R. brasiliensis was most closely related to Oldenlandia corymbosa. In a comparative analysis of chloroplast genome variation showed little variation among congeneric taxa, whereas variation was observed among genera in both coding and noncoding regions. In addition, comparisons of IR junctions (JLB, JSB, JSA, and JLA) revealed interspecific differences in the positions of genes such as rps19, ndhF, and ycf1, suggesting the possibility of boundary shifts at the IR junction regions. Because this study included only seven taxa of Spermacoceae, denser taxon sampling with additional chloroplast genome data will be necessary to better resolve relationships and to evaluate structural variation across the tribe. Nevertheless, the complete chloroplast genome of R. brasiliensis and the comparative results presented here provide a useful reference and a foundation for future phylogenetic and evolutionary studies of Spermacoceae.