This is a widespread weedy taxon that may be "native" in both North America and Eurasia. Although a narrow definition of biennis is followed here (as in W and elsewhere), distinction of closely related species may usually prove impractical in Ky. (grandiflora, nutans, villosa and parviflora). The potential species within this complex usually produce seed that is genetically identical to parents, due to "permanent translocation heterozygosity" but occasional hybrids do occur (Greiner 2008, Johnson et al. 2011, Rostański & Verloove 2015). In its strict sense, O. biennis is a widespread tall native annual or biennial weed (with petals ca. 1-2 cm long) that appears to have originated from hybrids of villosa and nutans (Dietrich et al. 1997). There is some potential for viable backcrosses of biennis with the two parents (Greiner 2008), but the situation in wild populations remains unclear. There are two cytological types of biennis, with switched maternal and paternal origins, but attempts to distinguish these morphologically (e.g. as ssp. centralis Munz and ssp. caeciarum Munz) have not been successful. Pre-flowering plants of Oenothera biennis are similar to those of the strictly biennial Gaura biennis. Leaves differ in their dull green upper surfaces (versus deep glossy green), their denser pubescence (often with distinctly bimorphic hairs ca. 0.1-0.25 mm and ca. 0.75-1.5 mm), and their margins with more remote and less distinct denticulations. Stems tend to be more erect, with less wide branching. O. biennis has an ancient tradition of use for food and medicine (Gaertner 1968, Moerman 2009, Singh et al. 2017).