Geographic variations in leaf shape of Acer ginnala (Aceraceae)

Acer ginnala Maxim. is distributed extensively throughout China; its leaf shape varies with region. Graphical and statistical methods are used to analyze the variations in the leaf shape of A. ginnala across ten provinces (Heilongjiang, Jilin, Liaoning, Inner Mongolia, Shanxi, Shaanxi, Shandong, Anhui, Jiangsu, and Zhejiang) in China. A total of 405 specimens were studied from the ten provinces. Results show that the shape of A. ginnala leaf varies greatly across geographic regions and that the dissection of the leaf is more significant in high-latitude regions than in low-latitude regions. The leaves are more deeply incised in Shanxi than in Shaanxi, although these two provinces are similarly intermediate-latitude regions. Moreover, a positive allometric trend, where dissection is more significant in large leaves than in small ones, is found in all provinces, especially those in high-latitude regions. Further analysis of the above results suggests that the observed leaf shape differentiation may be caused by the isolation effect of the Yellow River, which obstructs the genetic exchange of A. ginnala. The geographic variation of its leaf shape could be divided into two groups, i.e., north China group and south-west China group, therefore these studies support A. ginnala to be treated as two subspecies, A. ginnala subsp. ginnala and subsp. theiferum.