Question

Why do some flowers bloom only at night? Is there a biological reason?

Answer 1

Hylocereus undatus and others is a classic night blooming species. Flowers open at night and are wilted by dawn. Flowers are white and fragrant, as is typical of night blooming flowers, which are adapted to attract nocturnal pollinators such as bats and moths.
The bright colors that attract birds, butterflies and bees to flowers during the daytime are of little use in the dark. The eyes of bats lack the cone cells used to distinguish colors, but they have good discrimination of white versus black surfaces. In addition, bats have a moderate- to well-developed sense of smell, which they use to locate flowers and fruits. Similarly, night-flying moths depend heavily on their keen sense of smell to locate flowers.