* Yuan, Yao-Wu & Olmstead, Richard G. (2008): A species-level phylogenetic study of the "Verbena" complex (Verbenaceae) indicates two independent intergeneric chloroplast transfers.
* Yuan, Yao-Wu & Olmstead, Richard G. (2008): A species-level phylogenetic study of the "Verbena" complex (Verbenaceae) indicates two independent intergeneric chloroplast transfers.