Giant white moonflower

This is a species of night-blooming morning glory, native to tropical and subtropical regions of the New World, from northern Argentina north to Mexico and Florida. The flowers open quickly in the evening and last through the night, remaining open until touched by the morning sun. On overcast days, the blossoms may remain open for longer. The flowers also tend to remain open longer during cool temperatures - which may also cause the segments to snag or tear as they open.