Why Do Flowers Close Up at Night?

Many flowers have petals which are open during the day, but which close up at night. These flowers are reacting to light or temperature changes. Other flowers, however, remain open around the clock, while still others have unusual opening and closing habits. But these habits are all related to light or temperature changes.

Here’s how it happens. Heat makes the inner surfaces of a flower’s petals grow. So when the temperature goes down, the outer surfaces grow faster than the inner ones, thus making the flower close.

The crocus and morning glory, for example, open as the temperature increases during the day and close as the day gets cooler in the late afternoon.

On the other hand, the four-o’clock closes in the morning and opens again late in the afternoon, around four o’clock.

Then there is the moonflower and the night-blooming cereus, which keep their blossoms closed during the day and open only at dusk or at night.

Some plants even react to touch and actually close up their leaves and “play dead” if a hand or twig brushes against them!

Comments

  1. Anonymous says

    There must be an evolutionary advantage to the plant to have its flowers close at night. The existing article explains the mechanics of how it works; can somebody explain the “why”? What advantage does hte plant get by closing up at night?

  2. William Hand says

    It’s not just that it doesn’t explain the “why” of the process…

    …This doesn’t even explain the mechanics of it, though… If it was just a difference of growth connected to heat, then a night blooming flower couldn’t happen.

    Why even bother including this “expanation” if it’s gonna be such a friggin vacuous response to such a basic and interesting question?

  3. rob says

    from my understanding, keeping the answer to a few short sentences, this sort of behavior has to do with some evolutionary traits that should be deemed beneficial. one such trait is the fact that the open flower is used to attract some insects, namely bees, for the process of pollination. and most of these insects “perform their duties” strictly during the day time. also, many flowers send scents attracting these insects (along with their colors and the movement of the flower due to a breeze, as other means of attracting the attention of the insects). hence, the flower would benefit from closing at night to consume the limited resource of a scent when that resource cannot be used to its advantage.

    hope that helps a little bit

  4. Anonymous says

    Perhaps the plant is adapted to close at night to prevent moisture from reaching the reproductive whorls (i.e. stamens), which would lose function if they became too wet…

  5. Anonymous says

    as a qualified scientist i just gotta say, the internet really annoys me sometimes. What is the point of people posting things like “i reckon it’s gotta be blah blah blah” on sites such as these. It just makes it harder to find worthwhile information.
    I was curious about the ‘flowers closing at night’ phenomenon, it didn’t take too much surfing to come across the proper scientific term “nyctinasty” (look it up in wikipedia or better yet, a scientific literature database if you have access).
    The process is a finely tuned biochemical response (like most things in biology!) to circardian rhythms, very clever! Specific cells swell or diminish by altering salt content and thus eliciting fast movement of the leaf/petal.
    As for the evolutionary forces behind such an adaptation, i will leave that up to the ecologists to figure out : )

  6. Anonymous says

    Thank you for a proper explanation (or at least pointing out where a proper one can be found!). I’ve learnt a new word to be clever with :)

  7. Anonymous says

    I agree with the scientist about the mechanism of nyctinasty to explain the “how” (and thank you for the clarification). The “why” must be definitely due to an evolutionary advantage that aids plant reproduction. I am not sure about the conservation of scent, as some flowers that close at night do not produce a scent… but rely on colour to attract pollinators in the daytime. I read somewhere that the petals close to protect from cold, and that the temperature inside the flower can be several degrees warmer than the outside. The author then talked about insects enjoying the warmth (which I think is rubbish). Rather, I would suggest that the pollen distributed on the stigma must grow rapidly to fertilize the ovules usually located at the base of the carpel. This requires work of enzymes, and enzymes will operate optimally at a specific temperature range. Preservation of the internal temperature may promote growth of the pollen tube thus maximising the changes of pollination. I just made this up, but it would be easy enough to test it.

  8. Danc13 says

    Of course, why didn’t I think of that. God surely does it for no other reason than to entertain us. Idiot.

  9. Jason says

    @Danc13… God didn’t do to entertain us, He did it so the flower would be more protected at night and to protect the reproduction system. There are numerous benefits of the flower closing and just one more solid evidence of design. If the flower isn’t preserved, the ecosystem is at risk, and therefore the ability for the flower to close has an impact on many other organisms within the community (bees, foraging insects, etc). As always He built it as part of a complex and dynamic system with carefully crafted dynamic interactions. Again, further evidence of design. As to who the idiot is, I think your post made that clear.

  10. Camryn says

    I’m not sure but maybe it is because… the chloroplasts in the plant cell create photosynthesis, once the plant isn’t getting enough sunlight to create photosynthesis it must close down because it knows that its work for the day is done?

  11. Karen says

    I was trying to find out if Wisteria closes up at night or not. Does anyone know the answer? I’m editing a book and the author planted it in a night blooming garden. I’ve never grown the stuff so I could use the experience of someone who knows. Thanks!

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