Plant light sensors came from ancient algae. Duke Today, July 28, 2015. The light-sensing molecules that tell plants whether to germinate, when to flower and which direction to grow were inherited millions of years ago from ancient algae, finds a new study. The findings are some of the strongest evidence yet against the prevailing idea that the ancestors of early plants got the red light sensors that helped them move from water to land by engulfing bacteria, the researchers say.