Contribution of temporal floral closure to reproductive success of the spring-flowering Tulipa iliensis

Temporal flower closure is a non-morphological floral character of adaptive significance for growth of some species in extreme environments, and it has important implications for plant reproductive success. Flowers of Tulipa species responded to changes in temperature and closed temporarily at low temperatures, but they reopened when temperatures increased. In this study, we determined the effects of temporal flower closure of Tulipa iliensis Regel. on mating pattern, flower microenvironmental temperature, and sexual organ functions during exposure to low temperatures, rainfall, and wind. First, flowers of T. iliensis were incompletely herkogamous with stamens longer than the pistil. Floral closure resulted in the contact of dehisced anthers with the stigma and auto-pollen deposition on the stigma, thus facilitating automatic self-pollination. Second, floral closure maintained the temperature inside the flower, providing a stable microenvironment that promoted pollen germination and avoided a decline in stigma receptivity. Third, flower closure of T. iliensis before rainstorms avoided flushing of pollen from anthers and helped maintain both pollen viability and stigma receptivity during exposure to rain. Finally, flower closure maintained pollen clumping in the anthers during exposure to wind, thereby enhancing pollination efficiency by pollinators and/or automatic selfing. Therefore, temporal flower closure of T. iliensis is an important floral strategy in facilitating automatic selfing, extending the functional period of male and female organs, and it thus ensures reproductive success in the unpredictable early spring environment.