Evening Primrose (Oenothera elata)
Family: Evening Primrose (Onagraceae)
This is a big, bold flower, with blooms three or four inches across on a plant up to six feet tall. Most people miss it, though, because it spends its days with its flowers closed, sleeping off nights spent carousing with the hawkmoth, its favored pollinator. It's common in Yosemite Valley and spectacular enough to be worth hunting for around dusk, when the flowers open up for the evening. I've seen it along the fringes of the Yosemite Village day use parking lot and along Northside Drive approaching El Capitan.
Blooms: June - September
Oenothera elata etymology: Oenothera is a Greek term meaning "wine-scented," derived from the root word oinos (wine). Elata derives from the Latin word elatus, meaning high, elevated, or haughty, and presumably refers to the plant's height, since it doesn't exhibit obvious signs of hubris.
This Photo: In Yosemite Valley along Northside Drive near El Capitan, mid June