Flower orientation on slopes in the myco-heterotrophic species Monotropastrum globosum

摘要

We investigated the factors that determine the flower orientation of Monotropastrum globosum on a slope, and their effects on reproductive success. A previous study revealed that flowers on a slope faced the open space, which was presumed to increase pollinator attraction, and that orientation affected the reproductive success of individual flowers. When a plant has many inflorescences, interference among flowers may occur. We conducted a shading experiment to examine whether flower orientation changes in response to light conditions based on the angular distance between the slope and the flower direction (ADSF), and we analyzed the correlations between the position of individual flowers within plants, flower angle and ADSF, and the relationships between pollination and fruiting success and flower orientation. The shading experiment revealed that the flower orientation of M. globosum was affected by light, slope angle and flower position within a plant. The ADSF of the front flowers was smaller than that of the back flowers. However, flower orientation did not significantly affect either pollination or fruiting success, although the petal size of each flower did affect reproductive success. In M. globosum with multi-inflorescences, individual flowers may face the open space to reduce interference among flowers within an individual.