Oenother biennis is a native biennial plant or sometimes an herbaceous perennial. In the first year plants produce only a basal rosette of leaves that overwinter. In the second year a stem up to a meter or more in height arises from the center of the rosette bearing simple, alternate, pubescent leaves with widely spaced teeth. Leaves, especially basal rosettes, are often partly red or purplish. Flowers have 4 yellow petals, 8 stamens and one pistil with a 4-lobed stigma. A long tubular calyx extends far above the inferior ovary and the calyx lobes at the tip are strongly reflexed. The fruit is an elongate capsule opening at its tip to release numerous seeds. Flowering begins in late June or early July and continues throughout the summer to some degree. Fruit are long persistent on the stems which often remain upright throughout the winter.

Oenothera biennis is found nearly throughout Wisconsin on sunny, mostly dry, sandy sites, including a variety of man-made disturbances, but also on beaches and banks or ridges of streams or lakes.