This evening primrose (Oenothera biennis) grows along Tapawingo Drive in the Levee area of West Lafayette. Very common. Picture taken August 12, 2010.
There is another kind of Oenothera planted in the park nearby. Here is a link. They buy it, pay to plant it, pay to weed it. Oenothera biennis grows on its own, it costs nothing. Then they pay someone to mow it down.