"Immature flower buds of the sunflower do exhibit solar tracking and on sunny days the buds will track the sun across the sky from east to west and by dawn the buds will have returned to face eastward, like the leaves in the movie above. However, as the flower bud matures and blossoms, the stem stiffens and the flower becomes fixed facing the eastward direction." http://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/solartrack/solartrack.html
"Flowers of the wild sunflowers seen on roadsides do not follow the sun and their flowering heads face many directions when mature. However, their leaves exhibit some solar tracking."