Hylocereus undatus (Red Pitaya) is a species of Cactaceae

Commonly known as the dragon fruit

The nightblooming cereus is also known as the lunar flower, 'The queen of the night' or moon flower. This plant is native to the Sonoran Desert in North America. The plant grows as a thin, almost dead looking stick from a single stem in the ground. They bloom just on one or two nights of the year, typically around May 30. Beneath the ground is a large tuber, often the size of a watermelon, that was eaten by Indians and early settlers because of its nutritious content. Pack rats often eat these blossoms before morning, so catching a glimpse of them can be fleeting. They often stay open until the early morning hours, but then close up for another year.

http://annkschin.blogspot.com/2010/01/macro-monday-mid-night-glory.html