Variation in this widespread northeastern biennial needs further study. In Ky. it occurs typically within transitions from low woods to fields, often at upper edges of floodplains. Plants are highly palatable to generalist herbivores (from rabbits to Japanese beetles), and usually absent from pastured areas. Across its range the species varies greatly in habitat, leaf width and flower size (Munz 1965). Superficially distinct plants grow in the xeric dolomitic glades of se. CLAR (JC for KY) and Adams Co., Ohio (e.g. colls. of A. Cusick at Ohio State Univ.), and in dry sites elsewhere. These plants tend to have unusually small flower parts and narrow leaves (no more than ca. 8-10 mm). G. biennis, together with the more midwestern longiflora, the more southeastern G. angustifolia Michx. and related western species, appear to a form a somewhat intergrading complex; 2n = 14 in these and most other species of Gaura. However, biennis has unusually complex chromosomal structure, which may reduce hybridization and recombination (Raven & Gregory 1972). The genus Gaura has been recently combined with Oenothera in preparation for FNA (Levin et al. 2004, Wagner et al. 2013; W). Although nested within the complex reticulate phylogeny of Oenothera sensu lato, Gaura remains a distinct section; and other sections may still warrant genus status. Gaura is distinguished by its indehiscent fruits (versus dehiscent), with 1-6 seeds per capsule (versus 10-50+), each 1.5-3.5 mm long (versus 0.3-2 mm). See notes under Oenothera biennis on distinction from G.biennis without flowers.