Peniocereus greggii. Also known as Reina de la Noche, Queen of the Night. These plants bloom only once a year for a single night, perhaps twice occasionally, in the summer. The blossoms open after dark. They are pollinated by moths, and have a wonderful fragrance. The rest of the year, the plant just looks like a skinny dead cactus with branches. This year, some of the plants bloomed one night, and the rest, the next night. I went on the second night. Shortly before sunset, they got a horrible hailstorm that destroyed some of the buds. Very few were open when I was there; I only saw two completely open perfect flowers. Taken at Tohono Chul Park, Tucson, Arizona, USA. "Tohono Chul" means "desert corner" in the language of the Tohono O'odham (Desert People).