Calylophus serrulatus (Nutt.) P.H. Raven

Calylophus serrulatus (Nutt.) P.H. Raven. Oenothera serrulata is a species of flowering plant in the Onagraceae known by the common name yellow sundrops. Other common names include halfshrub sundrop, serrate-leaved evening primrose, shrubby evening primrose, plains yellow primrose, and halfleaf sundrop. It is native to central North America, including central Canada and the central United States.