The word 'nastic' is a term having to do with movement. It is the same term used to make up the word "gymnastic." Nastic movements are usually a response to something in the environment, light (photonasty) or water (hydronasty) or chemicals (chemonasty) or temperature (thermonasty), among others.
Many, if not most, water lilies are subject to nyctinasty, which are movements in response to the onset of night or the dark. This time of year, I usually plan a trip to the Kenilworth Aquatic Gardens, run by the Park Service on the edge of the Anacostia River in Washington. It doesn't pay to arrive too early in the morning, however, because most water lilies remain closed until the sun touches them.
My wife has a little pot pond on the deck with one goldfish that survived the winter and a lily which we bought early in the spring. It flowers and exhibits nyctinasty behavior, opening after the sun is well up and closing again by mid afternoon.
The movements are caused by a specific type of tissue in the base of the leaves that are subject to circadian rhythms. The native plant, bloodroot, exhibits this same behavior.
The first time I became aware of it was while I was filming bloodroot blossoms. When I first arrived at the bank in the woods where I had discovered them, the blooms were all closed.
When the sunlight touched them, however, you could actually watch them open almost like watching a time-lapse film. They would go from completely closed to fully open in no more than a minute. Like little diamonds, God's creation holds so many fascinating facets!
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