A Missouri native!
 
Missouri evening primrose (Oenothera missouriensis syn. Oenothera macrocarpa) is a sprawling herbaceous perennial with multiple stems that trail along the ground. Often seen festooning the tops of bluffs and rocky road cuts. Blooms May through August. Flowers are solitary, very large (up to 4 inches wide), 4-petaled, and bright lemon yellow. Often there are many blooming at once, making this a very showy plant. The flowers last only a day, usually opening in late afternoon and staying open until the next morning. Leaves are narrow and lance-shaped.
 
Height: 1 foot
Width: 1 - 1.5 feet
Full Sun