Oenothera ammophiloides R. R. Gates & Catcheside var. flecticaulis (R. R. Gates) R. R. Gates; O. ammophiloides var. parva (R. R. Gates) R. R. Gates; O. angustifolia Miller; O. angustissima R. R. Gates; O. angustissima var. quebecensis R. R. Gates; O. apicaborta R. R. Gates; O. atrovirens Shull & Bartlett; O. biennis Linnaeus var. cruciata (Nuttall) Torrey & A. Gray; O. biennis var. parviflora (Linnaeus) Torrey & A. Gray; O. biformiflora R. R. Gates; O. cleistantha Shull & Bartlett; O. comosa R. R. Gates; O. cruciata Nuttall; O. cruciata var. sabulonensis Fernald; O. deflexa R. R. Gates; O. flecticaulis R. R. Gates; O. hazeliae R. R. Gates; O. hazeliae var. parviflora R. R. Gates; O. hazeliae var. subterminalis (R. R. Gates) R. R. Gates; O. intermedia R. R. Gates; O. laevigata Bartlett; O. laevigata var. scitula (Bartlett) R. R. Gates; O. laevigata var. similis R. R. Gates; O. novae-scotiae R. R. Gates; O. novae-scotiae var. distantifolia R. R. Gates; O. novae-scotiae var. intermedia (R. R. Gates) R. R. Gates; O. parva R. R. Gates; O. parviflora subsp. angustissima (R. R. Gates) Munz; O. parviflora var. angustissima (R. R. Gates) Wiegand; O. robinsonii Bartlett; O. rubricapitata R. R. Gates; O. scitula Bartlett; O. subterminalis R. R. Gates; O. venosa Shull & Bartlett; Onagra biennis (Linnaeus) Scopoli var. cruciata (Nuttall) Britton; O. chrysantha Spach var. cruciata (Nuttall) Spach; O. cruciata (Nuttall) Small; O. parviflora (Linnaeus) Moench

Herbs biennial, sparsely strigillose, glandular puber­ulent, and villous with pustulate or non-pustulate hairs, sometimes predominately strigillose proximally or predominately villous with pustulate or non-pustulate hairs distally, glabrous, or some mixture of strigillose, glandular puberulent, or sparsely villous distally, sometimes appearing glabrous to the naked eye. Stems erect, green or red on proximal parts or throughout, mostly branched from base or only in distal 1/2, 30–150 cm. Leaves in a basal rosette and cauline, basal 10–30 × 1–4 cm, cauline 4–18 × 1–3 cm; blade usually bright green, sometimes pale green distally, white- or red-veined, narrowly oblanceolate, narrowly elliptic to lanceolate, or oblong, margins usually flat, rarely undulate, regularly dentate to remotely denticulate, sometimes teeth widely spaced; bracts persistent. Inflorescences erect or ± curved, unbranched or with secondary branches just proximal to main one. Flowers opening near sunset; buds erect, 3–5 mm diam., with free tips subterminal, spreading to erect, 0.5–5 mm; floral tube 22–40 mm; sepals green to yellowish green or flushed with red or dark red, sometimes only red-flecked, 7–17 mm; petals yellow to pale yellow, fading pale yellow to pale yellowish orange, very broadly obcordate, 8–15(–20) mm; filaments 7–13 mm, anthers 3.5–6 mm, pollen ca. 50% fertile; style 25–50 mm, stigma surrounded by anthers at anthesis. Capsules erect or slightly spreading, usually greenish black when dry, narrowly lanceoloid to lanceoloid, 20–40 ×3.5–5 mm, free tips of valves 1–1.5 mm. Seeds 1.1–1.8 × 0.5–1 mm. 2n = 14.

Flowering Jun–Aug. Open or disturbed, sandy or gravelly sites, roadsides, fallow fields, clearings, riverbanks, along water courses, salt marshes, coastal meadows; 0–1700 m; B.C., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Conn., Del., D.C., Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Pa., R.I., Tenn., Vt., Va., W.Va., Wis.; introduced in Europe, Asia (ne China, Japan), s Africa, Pacific Islands (New Zealand), Australia. It is introduced in British Columbia.

Oenothera parviflora is a PTH species and forms a ring of 14 chromosomes in meiosis, and is self-compatible and autogamous (W. Dietrich et al. 1997). It has plastome IV and a BC genome composition.

Onagra chrysantha Spach 1835, not Michaux 1803, is a superfluous name, as is Onagra chrysantha var. parviflora (Linnaeus) Spach, and both pertain here. O. biformiflora var. cruciata R. R. Gates is an invalid name that pertains here.