Why do some flowers close their petals at night, while others don't?

I've been wondering that, and no one seems to know the answer. Do you know?

Why do some flowers close their petals at night, while others don't?
Petal closure serves various purposes in plants, but no one knows for sure all the various "whys". Some flowers, like one of the waterlily genera, Nymphaea, seem to trap insects inside, apparently improving pollination rates. Others open and close on a temperature cycle.





The how is easier -- it's either change in osmotic potential or differential growth, depending on the species.





Fairly recent and readable review of the subject:


http://jxb.oxfordjournals.org/cgi/conten...
Reply:I'm still blossoming petal. My Boris says so anyway-and he wouldn't lie about something like that.
Reply:I was told that it's to protect the sensitive parts from grazing animals. Since pollinating insects can't see a flower at night there's no reason for it to stay open, so it might as well close.
Reply:it's just the way they are.
Reply:For the same reason certain flowers only pop up for a week then go away: Environmental Conditions
Reply:it has something to do with the sunlight. Opening the petals causes the flower to absorb the light but at night they close because they don't have to absorb any.

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