Contact: Richard Hund
American Journal of Botany
Caption: An hour before dawn, this sunflower (Helianthus annuus) plant has oriented its leaves towards the east in "anticipation" of sunrise. Sunflowers are well known for the robust solar tracking or heliotropism behavior they display through the course of a day to keep their leaves more-or-less perpendicular to the sun's rays for maximizing photosynthesis. These leaf movements are also regulated by the plants circadian clock, which allows the movements to commence in apparent anticipation of sunrise, as illustrated in the cover image. Contrary to popular belief, sunflower flowers do not follow the sun and usually face eastward. In this issue, Whippo and Hangarterís historical analysis of Darwinís interest in plant movements shows that his plant studies played a seminal role in the development of his general theory of evolution. Darwin studied plants to understand the physical and physiological basis of plant movements or behaviors to help support his ideas for how natural selection led to the evolution of animal behaviors. This image is from a time-lapse sequence that can be viewed at along with many other plant movement movies.
Credit: Photo credit: R. P. Hangarter.
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Related news release: Charles Darwin: More than the origin