Nyctinasty

Quit yer giggling, some of you! "Nyctinasty", or "nyctinasties" in its plural from, is not etymologically based where you're thinking, but on the root word "nastic"; of, relating to, or constituting a movement of a plant part caused by disproportionate growth or increase of turgor in one surface.  "Nyctinasty", a new word for ProfessorRoush's vocabulary, is the term for the circadian movement of plants (such as the closing of flowers or reorientation of a leaf position) that occurs in response to changes in light intensity and temperature.  This circadian rhythm is carried out by by a special organ in some plants named the "pulvini", a swelling at the base of a petiole or petiolule.  

For those "in the know", as you now are, nyctinasty differs from tropism, which is the term for plant movement in response to growth stimuli, such as when sunflowers follow the sun.

'Prairie Moon' at night

I was prompted to look up and learn the proper label for the phenomenon because I noticed for the first time, that when the peony 'Prairie Moon' bloomed it closes its flowers each evening; something I learned out of frustration one night when I thought, "hey, 'Prairie Moon' is probably blooming at its peak and I should get a picture and blog about it."  Needless to say, I learned something new that very night about this cultivar after its many years in my garden, and I had to go back the next morning to photograph its open and voluptuous blossoms.   The photos here in this blog entry were taken the same day; the "open" photos at 3:25 p.m. and the "closed" at 7:38 p.m.   Interestingly, in my blog about 'Prairie Moon' on 5/3/2023, there are photos of both closed and open states, but I was evidently curiously incurious about the process then.

If you read the Wikipedia entry for nyctinasty, it will veer into a sleep-inducing paragraph of phytochromes and protein Pr and PFr states and potassium gradients, but all those subcellular processes add up to the fact that in the pulvini, water moves into the lower cells (ground-sided), swelling them and closing the petal. Wikipedia also tells me that an alternative mechanism exists through hydrolysis of bioactive glycosides.  I am fortunate to have a scientific education that helps me understand all this, but I am also fortunate that understanding the process doesn't diminish the wonder and "awe" of it for me.  "The heavens declare the glory of God; and the firmament showeth his handywork": Psalm 19:1 KJV.

'Prairie Moon' midday

Online sources theorize that nyctinasty is likely a response to preserve pollen, decrease nightly predation, and minimize temperature decreases and water loss at night.   It occurs in many plants, but I haven't see Paeonia list among those.  Most legumes close their leaves at night.  Flowers that close at night include daisies, California poppy, Lotus, Rose-of-Sharon, Magnolia, Morning glory, and Tulips.  Some flowers, pollinated by moths or bats exhibit nyctinastic flower opening at night (for example the Nicotiana).

Anyway, now you know.  If you're looking for me at dusk, at least for a few weeks, you'll find me in the garden looking for nyctinastic behavior in other peony species.  I think 'Prairie Moon' may be unique in that respect, at least in my garden.