Just like humans and animals, plants have an innate ability to measure time. While they don’t have a central nervous system, they do tune themselves to a circadian rhythm much as we do. These circadian rhythms—or biological clocks—respond to light and temperature signals to regulate essential plant functions such photosynthesis, seed germination and growth, opening and closing their leaf pores, flowering, and senescence. Scientists were surprised to learn that even a plant’s roots actively respond to circadian signals.
Read more here: On the Clock