Oenothera fremontii S. Watson, Proc. Amer. Acad. Arts 8: 587. 1873; Megapterium fremontii (S. Watson) Britton

Herbs densely strigillose. Stems numerous, with numerous short secondary branches, 3–30 cm. Leaves gray, (2.8–)3.7–11 × 0.1–0.6(–1.5) cm; blade linear to narrowly elliptic to narrowly elliptic-lanceolate or narrowly oblanceolate, margins flat, entire or inconspicuously denticulate, apex acute. Flowers: buds with unequal free tips 1–2(–5) mm; floral tube (21–)35–65(–80) mm; sepals (20–)25–30(–37) mm; petals (17–)25–33(–37) mm; filaments 13–18 mm, anthers 10–12 mm; style (45–)55–80(–98) mm. Capsules ellip­soid to narrowly ellipsoid, often twisted, wings 2–5(–9) mm wide, body 13–30(–65) × 2–6 mm. 2n = 14.

Flowering May–Aug. Rocky soil derived from fine-textured sandstone, shale or chalk on rocky hillsides, bluffs, badlands; 400–900 m; Kans., Nebr.

Subspecies fremontii occurs from Franklin and Webster counties in south-central Nebraska south into Kansas to Ellsworth, Hodgeman, and Logan counties; also with disjunct locations in Antelope and Cedar counties in northeastern Nebraska, and Barber County in south-central Kansas. Some specimens from the eastern part of the range, where subsp. fremontii and subsp. macrocarpa are sympatric, appear intermediate between the two subspecies and are difficult to assign.