Floral differentiation among insular and mainland populations of Weigela coraeensis (Caprifoliaceae)

We compared the floral morphologies, floral scents, and flower visitor compositions of Weigela coraeensis var. coraeensis on the Japanese mainland and its variety fragrans endemic to the Izu Islands to examine the differentiation process of W. coraeensis var. fragrans. The corolla lengths of W. coraeensis were smaller on the Izu Islands than those on the mainland and decreased gradually with the distance from the mainland, probably resulting from changes in pollinator fauna. A total of 13 volatile compounds were identified in the floral scent analyses, and limonene was produced at the highest level, although the floral scents were not different between var. coraeensis and var. fragrans. In this study, it was suggested that the pollinator fauna peculiar to the Izu Islands influenced the morphological differentiation of W. coraeensis var. fragrans.