Common evening primrose (Oenothera biennis)

Common evening primrose photograph;  MN DNR, G. N. Rysgaard

Tall biennial, growing 2-6' on disturbed dry ground. Blooms mid to late summer. Yellow flowers with four petals open at dusk as the flower is pollinated by night-flying moths and insects. Alternate lance-shaped leaves have wavy, toothed margins. The stem is often reddish. Roots are edible.