We first conducted a likelihood ratio test  to determine whether our sequence data were evolving in a clock-like fashion. Because rate constancy along all branches of the phylogeny was rejected (δ = 146.63, d.f. = 14, P < 0.0001), we used a Bayesian relaxed clock methodology as implemented in BEAST v1.8.2  to generate a dated phylogeny for Coptis. Based on our recent broader study of Ranunculaceae , the split time between Coptis and Xanthorhiza was estimated at ca. 16.23 Ma (95% highest posterior density (HPD): 8.51–25.96) and was here used as a secondary calibration point. Following the suggestion of Ho , we assigned a prior normal distribution for the calibration, in which a standard deviation of 2 was set.