Some of our tulips are now out, merrily opening & closing their blooms according to their own schedule. What is it that drives this schedule?
The tulips have their own biological clocks built in; this is what drives the circadian rhythm of flower opening & closing. The tulip’s clock is reset everyday by the rising of the sun; the tulip can also move its position with the sun. This is photonasty or the tendency to physically respond to light stimulus. The tulips also demonstrate thermonasty, a response to temperature; tending to close up with a fall in temperature. Thus on a warm bright morning the tulip flowers open up beautifully but as light & temperature drop in the evening, they close their blooms again. Why have they evolved to do this?
The tulip flower is insect pollinated and the tulip advertises with both bright colours & scent from volatile oils. The picture above shows the male & female structures, with much pollen in evidence. To remain open overnight is to both risk damage from the weather & to waste volatile scents, whilst it’s insect pollinators are not around. Thus a tulip increases its chances of successful reproduction by closing it’s blooms at night. Many flowers show this behaviour and conversely, for example, bat pollinated plants often only open their flowers at night.
Plants also use biological clocks to sense various other things such as opening leaf stomata just before dawn ready for photosynthesis and by monitoring day / night length they can tell whether its flowering season or not.
Read on to view a video …