Oenothera biennis L.
Onagraceae (Eveningprimrose family)
Usually an erect biennial or winter annual. Occasionally a summer annual.
Alternate, narrow oval-shaped, smooth to slightly wavy leaf margins, with distinctive pink to white midveins. Leaves initially develop from a basal rosette.
Erect, semiwoody, approaching 5 feet in height. Stem usually branches only at the top and may be visible through the winter.
Flowers and fruit
Flowers are yellow, attached to fused sepals forming a tube and found in terminal spikes. Seed capsules are woody, cylinder-shaped and thickest near the bottom.
Cutleaf eveningprimrose (O. laciniata Hill)
Differs by having a prostrate to moderately erect, branching stem; wavy and coarsely toothed leaves; yellow to reddish flowers in the upper and middle leaf axils; and linear, cylinder-shaped seed capsules.