Geographical variation in flowering phenology of Dianthus japonicus Thunb. in western Japan

Abstract

We investigated the flowering phenology of Dianthus japonicus in the Pacific and Seto Inland Sea regions of western Japan. Field surveys revealed a distinct three-month divergence in flowering periods: populations along the Seto Inland Sea coast bloom in early summer (June–July), while those along the Pacific coast bloom in autumn (September–October). This differentiation was maintained in a common garden experiment, suggesting that the trait is genetically differentiated. This phenological variation likely results from adaptation to regional climatic characteristics: drought avoidance during the dry summers of the Seto Inland Sea and utilization of the high-rainfall environment of the Pacific coast. The observed divergence in flowering phenology represents a significant case of life-history divergence driven by the diverse climatic conditions of the Japanese archipelago.