What are 'moon flowers' and why do they bloom only at night?

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'Moon flower' is the common name for a variety of plants that have flowers that open at night. These flowers are big and white. In Arizona we have several of these types of flowers. There are the sacred datura (Datura wrightii), night-blooming Cereus (Peniocereus greggii), and several species of morning glory (Ipomoea). These plants have evolved over millions of years to be timed with the night/day cycle to open only in the night. They do this because night-flying insects mostly pollinate them. One such insect is the hawk moth. The flowers are sensitive to small changes in light so that they are open when these insects are out in the evening. An interesting science project would be to see what happens if you change the lighting conditions for these types of flowers.

Moon flower image by Bob Peterson

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