We sampled all 15 species of Coptis recognized by Tamura . Coptis and the monotypic Xanthorhiza Marshall compose the subfamily Coptidoideae, which is sister to a large clade containing the overwhelming majority of genera of Ranunculaceae [24, 25]. Scoring this large clade for geographic areas is a challenge. Here, we only selected Xanthorhiza as the outgroup. The sampled species and their GenBank accession numbers are listed in Additional file 1: Table S1.