Fig. 6

Results of Principal Component Analysis (PCA) of the symmetric component (a) and asymmetric component (b) of leaves of two Quercus aquifolioides lineages (WSP-HDM and Tibet) and mixed individuals. Scatter plots of PC1 and PC2 scores, with 95% confidence ellipses in a. Transformation grids for the left and right graphs represent shapes corresponding to extreme negative ( −) and positive ( +) PC scores. Symmetric component (a) of PCA formed Tibet and WSP-HDM as distinct groups with some overlap, while the mix group was scattered between the two lineages. Along PC1, the change of leaf shape from subelliptical to suborbicular form was primarily related to the shape of the apical and basal regions and the length of petiole. The variation along PC2 mainly associated with the position of the maximum width of the leaf. For asymmetric component (b), all the specimens overlapped almost completely and the three lineages could not be discriminated, as has already been reported in several previous studies (Viscosi and Cardini 2011; Viscosi 2015; Liu et al. 2018). In detail, the variation along PC1 was mainly the changes in the relative position of the left/right sides at the maximum width of the leaf blade and the differences in the relative sizes of the leaf blade, whereas the variation along PC2 principally focused on the bending direction of the leaf blade toward left or right in asymmetric component