plants falling asleep

White Oxalis purpurea closing up for the evening

White Oxalis pur­purea clos­ing up for the evening.

Detail of white Oxalis pur­purea think­ing about some shut-eye.

Purple-leaved Oxalis pur­purea clos­ing up in the late after­noon shade.

A lot of the flow­er­ing plants in the gar­den don’t bother open­ing their petals until the sun’s up and then shut their flow­ers as soon as the light begins to fade and tem­per­a­tures drop in the after­noon. Over the week­end I was notic­ing this going on with my oxalis plants and, less dra­mat­i­cally, with my arctotis.

There must be a name for this behav­ior, I thought, and so off I went look­ing for an answer. Before long up pop three inter­est­ing words: pho­tonasty, ther­monasty and nycti­nasty.

Accord­ing to one of the sources, the Text­book of Botany by Chhat­wal and Singh, pho­tonasty hap­pens when a plant senses light and reacts to it by open­ing or clos­ing its flow­ers. Because of this, morn­ing glo­ries open in the…well, morn­ing. Then there’s ther­monasty, where flow­ers react pri­mar­ily to tem­per­a­ture. Tulips will open with a rise of 2–3 degrees Cel­sius, while a cro­cus will zip open when the tem­per­a­ture rises just a half degree.

And then there’s the more com­plex phe­nom­e­non of nycti­nasty, which “is influ­enced by the inten­sity of light and also tem­per­a­ture dif­fer­en­tials, the for­mer stim­u­lus being more pow­er­ful and effec­tive. The foliage leaves and also the flo­ral leaves in many species of plants…attain dif­fer­ent posi­tions at day time and at night viz dur­ing the day, the leaflets remain open or spread up in case of Oxalis, clever beans, alfalfa, etc., while by the onset of dark­ness they close down. This is also known as sleep movement.”

Yes­ter­day after­noon was pretty bright, but cool. The oxalis barely opened before shut­ting back up. So it requires both heat and warmth to open fully. So nycti­nasty makes sense. The arc­to­tis seemed to open more fully, ear­lier in the day. My guess is that they respond more sim­ply, mainly to light, which would mean that they exhibit pho­tonasty. (What’s truly going on could be lots more com­plex than this and really might only be solved by exper­i­men­ta­tion, a point made in an arti­cle, “Flower open­ing and clo­sure: a review” by Wouter G. van Doorn and Uulke van Meeteren in the Jour­nal of Exper­i­men­tal Botany. Read the inter­est­ing text [ here ].)

Next I need to find out what “clever beans” are.

In my web trawl it turns out I’m not the only gar­den blog­ger look­ing at this phe­nom­e­non this week. Tilthy Rich took a quick spin around nycti­nasty [ here ]. Maybe he has the same plants bloom­ing, mak­ing him ask the same questions…

Flow­ers of Arc­to­tis acaulis ‘Big Magenta’ begin­ning to fold up for the night.

Another clone of Arto­tis acaulis clos­ing up in the after­noon: Pho­tonasty? Ther­monasty? Nyctinasty?


February 08 2010 06:30 am | Categories: gardening • my garden | Tags: • • • • •

13 Responses to “plants falling asleep”

  1. Noelle/azplantlady on 08 Feb 2010 at 9:44 am #

    Thank you for such an infor­ma­tive and inter­est­ing post. I do enjoy my flow­ers that do close at night, but didn’t real­ize that there may be dif­fer­ent stim­uli that they respond to — open­ing with a half-degree dif­fer­ence in tem­per­a­ture? Amazing…

  2. ryan on 08 Feb 2010 at 9:53 am #

    I might have to start using the word nycti­nasty more often. When we did the gar­den show a few years ago, a cou­ple of the natives wouldn’t open their flow­ers and petals all the way because the light wasn’t strong enough inside the build­ing. Though there was also a time of day or inter­nal clock thing hap­pen­ing, because they would open part way by mid-morning, even though the light lev­els hadn’t changed for sev­eral hours.

  3. Sunny on 08 Feb 2010 at 12:00 pm #

    Lovely post, intrest­ing pho­tos, taken beautifully:)

  4. Elephant's Eye on 08 Feb 2010 at 12:25 pm #

    And one day, if you come to Namaqua­land in the North­ern Cape (South Africa) to see those flow­ers at home in the spring — you go out to look at flow­ers between 10 and 4. They keep very civ­i­lized hours. If it is over­cast, or windy — then they don’t get out of bed. But when it all comes toghether …

  5. tina on 08 Feb 2010 at 2:47 pm #

    Plants are just amaz­ing things to be so sen­si­tive to their surroundings.

  6. susan morrison (garden-chick) on 08 Feb 2010 at 5:35 pm #

    James, I love it that when you notice some­thing inter­est­ing hap­pen­ing, you actu­ally take the time to research it. I must con­fess that unless the infor­ma­tion comes to be in an absolutely effort­less way, I am much too lazy to find out more.

    Which of course, is why I visit here.

  7. Carol on 08 Feb 2010 at 6:30 pm #

    Won­der­ful post James! It is so inter­est­ing to observe plants and to learn about their inner clocks and intel­li­gence. Botany is a fas­ci­nat­ing sub­ject. ;>)

  8. Carol on 08 Feb 2010 at 6:32 pm #

    I for­got to say … your pho­tos are stun­ning… Love the first one espe­cially! Great title too!

  9. lostlandscape on 08 Feb 2010 at 8:02 pm #

    Noelle, I was sur­prised myself. I thought it was just day­light. But then on bright but cold morn­ings I have a hard time get­ting out of bed, so it makes sense that there’s more going on than just sunlight.

    Ryan, I hadn’t thought of this in the con­text of gar­den shows or gar­den shows where the dis­plays are all shaded. It’d be cat­a­strophic to do an amaz­ing gar­den design where the flow­ers failed to open!

    Sunny, thank you!

    EE, what you say about the wind reminds me of the one trip I took to the Cal­i­for­nia Poppy Pre­serve. After trav­el­ing 4 hours from my home on a cold, stormy day, I learned that Cal­i­for­nia pop­pies are one of the plants that keeps their flow­ers closed in inclement weather–like some of the plants in your Namaqua­land dis­plays. What a dis­ap­point­ment that was.

    Tina, I agree. The more I find out about plants the more inter­est­ing they become.

    Susan, I have a bit of a lazy streak too. It took me how many decades to finally research this one? But I hope you’ll indulge me the occa­sional post with pretty pic­tures but with zero infor­ma­tion content…

    Carol, thanks! That first is my favorite of the bunch as well. The lit­tle tubu­lar buds on the oxalis are pretty cool how they shade from white to yel­low to green.

  10. skeeter on 09 Feb 2010 at 11:14 am #

    I view these plants like peo­ple. Some peo­ple are full of energy and can go with lit­tle sleep, while oth­ers need more rest to be able to live up to their full poten­tial when awake. :-) . In some coun­tries they have long lunch hours so peo­ple can take a nap. These plants just don’t wake up from their nap until the next day…

  11. country mouse on 10 Feb 2010 at 4:16 pm #

    I love botan­i­cal lan­guage. But I think phot­nasty is when I for­get to clean my lens and there’s a big blob on all the images from a shoot!

    BTW our blog was tagged with an “Hon­est Scrap” award by Chris­tine at Idora Design — I did the post for us mice and tagged you (and six oth­ers) in turn. Don’t feel oblig­ated — but have fun if you like.

  12. lostlandscape on 14 Feb 2010 at 3:32 pm #

    Skeeter, I like your take on this. Some folks (not me!) are major night owls, and there are plants like datura, night-blooming jas­mine or four o’clocks that don’t open up until near dusk but stay open late into the evening or the next morning.

    CM, I love the lan­guage too, and the fact that peo­ple have observed a behav­ior closely enough that they decided it needed a name. And thanks for the tag! I’ve sworn off memes, but I might assem­ble some­thing if time and inspi­ra­tion cooperate!

  13. love on 22 May 2010 at 10:38 pm #

    I’m doing this for a school project.
    Why don’t you add extra pic­tures or some­thing. The info is good. I love the pur­ple oxalis.

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