Fig. 1

a Colour-coded grouping of the 43 Machilus thunbergii populations according to STRUCTURE with the most likely group number K = 2. The colored pies were drawn on the China map which was downloaded from https://www.webmap.cn/;b histogram of the STRUCTURE assignment for all individuals at K = 2; c principle component analysis on pairwise genetic differentiation of populations. The red dotted line shows the northern boundary of tropical zone in broad sense [30, 36]