Project
Heliotropism in Trillium grandiflorum provides increased reproductive successHeliotropism of flowers has been repeatedly shown to provide a reproductive advantage to individuals. This fitness gain most often results from increased pollinator visits and/or the promotion of growth due the increased temperature that the flowers gain in the process. To date, almost all demonstrations of fitness advantages of heliotropism have focused on plants from the arctic or from alpine regions where a heat gain provides an advantage to the plants. In this study, we report heliotropism in the white trillium, Trillium grandiflorum, an early spring blooming species from the deciduous temperate forests of eastern North America. The white trillium has an horizontal seasonal heliotropism with flowers mainly facing South and showing little daily variation. The study of 479 tethered plants indicated that heliotropism provides a reproductive advantage to the white trillium with South-facing individuals showing a 12% increase in fertilized ovules compared to North-facing plants. If the fitness advantage of heliotropism is rarely reported for temperate forest species, the ecology of this long-lived perennial is, in many aspects, similar to the alpine and arctic heliotropic species. Indeed, white trilliums are insect-pollinated and they flower when the weather is still cold, before the trees leaf out. This suggests that there are potentially more species for which heliotropism is advantageous among early spring flowers from the temperate forest.
