Fig. 3.

a Colour-coded grouping of the 36 Euptelea populations according to the three structure clusters (I–III) (see Additional file 2: Table S1 for population codes). Red and black dashed lines are identified in Fig. 1. b Histogram of the structure analysis for the model with K = 3 (according to both lnP(D) and ΔK; see Additional file 7: Figure S2). Each vertical bar represents one individual. The assignment ratio of each individual into one of the three clusters is shown along the y-axis. Each cluster is represented by a distinct colour