Oxalis triangularis (Purple Shamrock) is a classic example of a plant which responds with movement to external stimulus. The leaves open and close in response to varying light levels with the result that they are open during during the day and close at night. This is true movement (i.e. not growth) and is non-directional with respect to the stimulus making it an example of nastic movement towards light: photonasty. One image captured every 30 seconds for about 1.5 hours, played back at 25 frames per second; ~750x actual speed. The exposure time was progressively increased through the video so the drop in ambient light levels are not seen.
