If you have never watched an evening primrose flower unfurl, you have missed a real treat http://www.youtube.com/watch?v=DiODdt8l108. I am willing to bet no matter what your age, you will get a "jaw-dropping" thrill from watching this phenomenon in person.
The Evening Primrose, Oenothera biennis, is mainly pollinated by the sphinx moth. It's a night bloomer that emits a delicate perfume to attract the moth. The pale yellow flower produced measures about two inches across. It has four petals, prominent stamens , cross shaped stigma, and a long green calyx. The flowers remain open from evening to early morning. The Evening Primrose plant itself is rather ugly, tall and weedy. To keep from pulling this "weed" out of my garden of cultivated plants, I have to keep reminding myself of its impending amazing show.