Helianthus nutallii (Nuttall's Sunflower)

From CONPS: A showy perennial (3-8') forming a clump of tall stems with brilliant yellow-gold flowers (3-4"), which will grow in clayey soils by short, shallow rhizomes (so it' easy to dig out.) Has opposite leaves, and should be grown in a moister area. Best in full sun. Blooms late - Important to fall migrating Monarch butterflies.