Maximizing Photosynthesis

• Plants that turn their leaves or flowers perpendicular to the sun are trying to maximize the amount of energy they capture from the sun and can, in turn, use for photosynthesis.
  
  

Preventing Overheating

• Some plants turn their leaves parallel to the sun at midday when the sun's rays are most intense, according to The Ladybird Johnson Wildflower Center, to reduce their exposure to sunlight and avoid damage.
  
  

Attracting Insects

• Flowers may also turn toward the sun to heat themselves, which makes them more attractive to insects and encourages pollination. In cold air, insects that are warmer are able to fly better.
  
  

Circadian Rhythms

• Solar tracking at night in anticipation of dawn may be related to circadian rhythms in which the plant prepares for the sun's appearance.
  
  

Sunflowers

• Although sunflower buds do orient themselves in relation to the sun, moving as the sun moves from east to west, mature sunflowers do not. Fully developed sunflowers face the same direction all day. (Visit http://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/solartrack/solartrack.html for a video demonstration of this phenomena.)