Seasonal Changes in Flower Characteristics of Oenothera laciniata Naturalized in Japan

Abstract

The present study aimed to investigate the possibility of partial outcrossing in Oenothera laciniata, which is a naturalized plant in Japan. We investigated the changes in the morphology of the petals, stamens, and pistils of O. laciniata flowers under different environmental conditions and seasons. Contrary to the existing knowledge that flowers of O. laciniata bloom at evening and nighttime, our study found that they also bloomed at daytime in April, when several insects visit these flowers. We found that the petal length was longer, that is, flower size is larger in April, than that in June and August. Flowers of O. laciniata likely attract pollinators by flowering at daytime with larger size in the spring season. Further, we found the occurrence of three atypical types of flowers in O. laciniata including 1) the pin type, which has longer stamens compared to pistils, 2) the thrum type, which has longer pistils compared to stamens, and 3) the close type, whose column head does not open. These atypical flowers likely help increase the opportunity of outcrossing, and cultivation test results suggest that they may be genetically associated. However, normal flowers also co-existed on plants with atypical flowers. The frequency of the occurrence of these atypical flowers were random and did not exhibit any trend with season or natural habitats. Based on these observations, we conclude that these atypical flowers are not distinctly distylous, but rather present a variation of form of the flowers of O. laciniata