Oenothera flava

Oenothera flava, the yellow evening primrose (a name it shares with Oenothera serrulata), is a species of flowering plant in the family Onagraceae. It is native to western Canada (except British Columbia), the western and central United States, and Mexico (except southeastern Mexico), and it has been introduced to the former Czechoslovakia. An almost stemless perennial reaching 20 cm (8 in), it is typically found in damp situations such as prairie swales, open woodlands, and alongside streams....read more on Wikipedia.