Oenothera caespitosa (White Evening Primrose, Tufted Evening Primrose)

This perennial occurs across the western United States, from 4000 to 7500 feet. From spring through late summer it produces masses of huge white flowers that open in the late afternoon and fade to pink by morning. The fragrant flowers can be 4 inches in diameter or more, and stand out against the large dark green leaves. Plant in full sun and well-drained soils.