ECOLOGICAL SIGNIFICANCE OF FLOWER HELIOTROPISM IN THE SPRING EPHEMERAL ADONIS-RAMOSA (RANUNCULACEAE)

Flower heliotropism could increase reproductive success in Adonis ramosa by increasing pollination, fertilization success, and/or seed development. Mean gynoecium temperature of heliotropic flowers was 5.5 degrees C warmer than the ambient. Under natural conditions, seed set was restricted by pollen limitation. Activity of pollinating insects was temperature-dependent and the visiting frequency was higher in heliotropic flowers than in non-heliotropic ones. As optimal temperature for pollen germination and pollen tube growth was higher than the ambient temperature, heliotropic warming might facilitate greater fertilization success after pollination. Experiments combining hand-pollination and petal removal showed that both seed set and individual seed weight decreased when heliotropic effects were removed. Thus, all three hypotheses were supported in this study. Advantages of out-crossing through heliotropic movements was not clear in this study, because there was no significant difference in individual seed weight between selfed and out-crossed flowers.