So many evening-primroses, so little time! Particularly since the flowers fade by mid-day. If I counted right, USDA lists 143 species in this bunch.I hesitate to call it a genus. Many botanists split Oenothera into three or four genera. When they do, this becomes Calylophus, because the stigma doesn't have longer, narrower lobes. Adding to the fun, this is also called yellow evening-primrose, yellow sundrops, halfshrub sundrops, serrate-leaf evening-primrose, shrubby evening-primrose, halfleaf sundrop, and plains yellow primrose. This is very much a species of those plains, growing in AR, AZ, CO, IA, ID, IL, IN, KS, KY(X), MI, MN, MO, MT, ND, NE, NM, OK, SD, TX, VT, WI, WY, AB, MB, ON, and SK. Sedgwick Co CO, 6/16/13.