Nyctinasty (flower response to light: opening with or closing without light) in hibiscus plants is a mechanism to protect against adverse conditions such as cool temperatures that can be damaging. Through a lack of light stimulus and circadian rhythms the plant is able to trigger the molecular movement of ions to allow for the closing of the flower.
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ISO 100, 1.3 sec at f / 29
Here are three macro photographs of this bloom, all from the Canon 100 “macro” lens. I start with the shutter diaphragm open at 4.0 (“F-stop”), a little narrower at 4.5 and a bit more at 9.0. For this lens the maximum opening is at 2.8, the narrowest is 32. As the opening narrows (F-stop increases) the exposure time needed to capture enough light lengthens and the range of the image in focus increases.
ISO 100, 1/30 sec at f / 4.0 
ISO 100, 1/25 sec at f / 4.5 
ISO 100, 1/6 sec at f / 9.0
References
Wikipedia – “hibiscus.”
Michael Stephen Wills Photography 
Beautiful macros! I seldom use anything beyond F/8 on my lenses. Have you tried long telephoto lenses for macros?
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I have one useful in a pinch.
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Interesting.I assume it is the same for day lilies that close once the sun has gone at the end of the day.
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similar, though day lilies do not reopen
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Yes they do not. And I have a bumper crop of lovely daylilies this year and every day I remove the faded blooms from the previous day. Now they are almost finished.
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Same her, Pam grows a variety in our rock garden
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I knew some flowers closed with the fading of light, but I didn’t know what that was called. I always learn something from your posts. I’ve never seen a yellow hibiscus. Lovely!
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