Flowers Opening and Closing
Why do some flowers close at night and open during the day?
see the following:
Plant movement responses to temperature (thermonasty) and daily rhythms of
light and dark (nyctinasty)
Anthony R. Brach, Ph.D.
There is a mechanism which causes this to happen, but
your question is why , not how, so I will respond to
It appears that animal and plant evolution has pointed
in the direction of survival and procreation. In the
case of both animals and plants, those activities
which promote survival and procreation endure and
others are lost by lack of survival or procreation.
The specific activity you mention involves
procreation. The theory is that a plant will have its
flowers open and available for fertilization by
insects, if that is the normal mode of fertilization
for the particular plant, and the flowers will close
at other times to conserve resources. In the case you
describe, it is likely that the insects which visit
and fertilize those flowers visit during the daytime
hours, so there is no benefit to the plant to have
them opened at night. A plant often produces scents
to attract insects, and if the flower closes at night
when the insect might not be around, resources are
conserved because the scent will not be wasted as it
volatilizes into the night air.
Naturally a lot of this is theory but it is
consistent with many of our own choices in life which
support our own survival with the least possible
expenditure of resources or energy.
Good question, thanks for using NEWTON!
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Update: June 2012