Description from Flora of China
Oenothera biennis Linnaeus var. parviflora (Linnaeus) Torrey & A. Gray.
Herbs erect, biennial, with taproot and basal rosette. Stems 30-150 cm tall, simple or sparsely branched, sparsely strigillose (sometimes only lower parts) mixed with glandular and long spreading pustulate-based hairs. Leaves bright green, with white or red veins, strigillose to subglabrous, sessile to shortly petiolate; rosette blade 10-30 × 1-4 cm; cauline blade lanceolate to narrowly elliptic or narrowly oblanceolate, 4-18 × 1-3 cm, base attenuate, margin dentate, apex acute. Inflorescence a dense simple or sparsely branched spike, apex often nodding or curved. Flowers open near sunset; floral tube 2.2-4 cm. Sepals 7-17 mm, with free tips 0.5-5 mm, ± subapical. Petals yellow to pale yellow, fading to orange or dull yellow, 8-15(-20) mm. Anthers 3.5-6 mm; pollen ca. 50% fertile. Ovary strigillose, with some spreading, pustulate-based, and/or glandular hairs; stigma surrounded by anthers. Capsules dark green, drying nearly black, narrowly lanceoloid to lanceoloid, 2-4 cm, sessile. Seeds in two rows per locule, brown to dark brown, 1.1-1.8 mm, irregularly pitted. Fl. Jul-Sep(-Oct), fr. Aug-Oct. 2n = 14, permanent translocation heterozygote; self-compatible, autogamous.
Open, usually disturbed sites, roadside ditches; near sea level to 1000 m. Hebei, Liaoning [Japan; native to E North America; widely naturalized in S Africa, Europe, and Pacific islands (New Zealand)].