Study of the sunflower movement may reveal clues regarding unknown mechanisms that regulate periodicity and spatial complexity in plant growth and development. In this paper, we introduce an automated process to track circumnutation of sunflower seedlings. The objective is to track the leaves of the sunflower plant in a video captured by an overhead camera. The tracking method presented predicts the translated and rotated boundary in the subsequent frames by active contour models. A salient feature of our solution is a constraint on affine transformation between updates. The constrained affine active contours used in this paper exhibit improvement over other traditional active contour approaches, with the new method yielding error less than one percent in the tracked sunflower centroid position.