Leaf Blade Thickness Differentiation between Coastal and Freshwater Populations of the Coastal Plant Vitex rotundifolia (Verbenaceae)

Vitex rotundifolia (Verbenaceae) is one of the coastal plants that commonly grows on sandy seashores, but also occurs at Lake Biwa, a freshwater inland lake. To assess morphological differentiation between coastal and inland individuals with regard to the leaf thickness, we mea- sured nine populations of Vitex rotundifolia from Lake Biwa, Ise Bay in Pacific Ocean side and Wakasa Bay in Sea of Japan side. We measured leaf blade thickness and applied one-way analysis of variance (ANOVA) to test the difference. Post-hoc multiple comparison resulted in four major groups recognizing all inland populations from Lake Biwa as a distinct group while affiliation of coastal populations was assigned to other three groups regardless to localities. Inland individuals tended to have thinner leaves, implying intraspecific differentiation due to adaptation to habitat environments.