Plants need their sleep too

A couple years ago I won an oxalis plant as a door prize at a Master Gardener meeting.  I removed it from the plastic pot it came in, put it in a pretty ceramic pot and placed it in my dining room near the window. 

For those not familiar with the plant, oxalis is sometimes called shamrock plant because of the shape of its leaves.  The leaves can be either green or purple and the delicate flowers are white or pink. 

            I’ve noticed something strange about the oxalis.  When I go into the dining room at night, the leaves are all folded into themselves and drooping, not like the plant is sick, but almost like it’s sleeping.   The next morning it’s normal again.  This happens every night.  When I have to go into the dining room at night, I almost want to say, “Oops, excuse me, sorry to bother you!”  I get what I need, turn out the light, and get out of the room as fast as I can.

            It turns out that there’s a word for the process that makes the oxalis leaves droop.  Nyctinastic.  It means night-induced movements. 

            If you grow a vegetable garden, you may notice that the leaves on your bean plants begin to droop near dusk.  Same thing.  They don’t need water, they just need sleep.  Wood sorrel is another plant that is nyctinastic.  You might find it growing as a weed in your flower beds.  The leaves look like miniature shamrocks and it has tiny yellow flowers. 

            Most plants in the legume family are nyctinastic to some degree.  These include alfalfa, clover, peas, beans, lupines and soy. 

            We don’t know why some plants are nyctinastic and others are not, but scientists have been studying how it happens since the 4th century BC.  Nyctinastic movement is regulated by chemical compounds that differ depending on the plant.   The plants all have leaf-closing substances and leaf-opening substances in competition.  When it starts to get dark, the leaf-closing substance is stronger and wins out.  When morning comes, it is out-competed by the leaf-opening substance. 

            Scientists have also discovered that when nyctinastic plants are subjected to sleep deprivation, they wither and die.  The plants need eight hours or more of sleep each night, just as we do.  This is a good incentive for unplugging electronics that light up your rooms at night and turning off outdoor lights.

The “nastic” part of the word means “a non-directional movement in response to a stimulus.”  Non-directional means that the plant is making a movement but not necessarily toward or away from the stimulus.

There are other “nastic” movements that plants make such as photonasty (response to light), chemonasty (chemicals), hydronasty (water), thermonasty (temperature), geonasty (gravity) and thigmonasty (touch).

You may not find any practical use for this knowledge, but you will impress your friends with your new vocabulary words!  Nyctinastic is pronounced “nick-tin-as-tick.”

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