Passion flowers have disc-like blooms with spiky anthers sticking up out of the middle. Passiflora edulis specifically is known for its round-to-oblong, juicy fruit. The fruit's rind may be either purple or yellow, after an immature green stage.
Purple and yellow passion flower blooms open and close at different times. Both the University of Hawaii Cooperative Extension Service and Purdue University say the purple passion flower is open between dawn and noon, and the yellow between noon and as late as 10 p.m.
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The difference in opening and closing times for the purple and yellow passion flowers makes cross-fertilization difficult, should you want to breed the two. Purdue University notes that a previous study by R.J. Knight suggests artificial light may help extend the amount of time the yellow passion flower is open.
Passion flower's tendency to open and close at specific times makes it a common sight in floral clocks. Floral clocks are groups of flowers that bloom at different times of the day, arranged to estimate the hour.