Calylophus hartwegii (Bentham) P. H. Raven subsp. lavandulifolius (Torrey & A. Gray) Towner &P. H. Raven; C. hartwegii var. lavandulifolius (Torrey & A. Gray) Shinners; C. lavandulifolius (Torrey & A. Gray) P. H. Raven; Galpinsia lavandulifolia (Torrey & A. Gray) Small; G. lavandulifolia var. glandulosa (Munz) Moldenke; O. hartwegii Bentham var. lavandulifolia (Torrey & A. Gray) S. Watson; O. lavandulifolia var. glandulosa Munz

Herbs perennial, densely strigillose throughout, some­times glandular puberulent distally; from a stout taproot. Stems several to many, decumbent to ascend­ing, branched, 4–20(–30) cm. Leaves 0.6–5 × 0.08–0.6 cm, fascicles of small leaves 0.2–1 cm often present in non-flowering axils; petiole 0 cm; blade narrowly lanceolate or narrowly oblanceolate, base attenuate to truncate, sometimes clasping, margins entire or subentire, sometimes revolute, sometimes weakly undulate, apex acute to obtuse. Flowers usually 1 per stem opening per day near sunset; buds with free tips 0.3–3 mm; floral tube 25–60 mm, funnelform in distal 1/2 or less; sepals 8–20 mm; petals yellow, fading pale pink or pale purple, 12–28 mm; filaments 6–12 mm, anthers 5–11 mm, pollen 85–100% fertile; style 30–75 mm, stigma yellow, quadrangular, usually exserted beyond anthers. Capsules 6–25 × 1–3 mm, hard, promptly dehiscent throughout their length. Seeds obovoid, 1.5–2.5 mm. 2n = 14.

Flowering Apr–Aug. Local and sparse, on sandy and rocky, calcareous soil, high plains, mountains, often with Artemisia tridentata, Cercocarpus, Juniperus, Pinus edulis, or P. monophylla, sometimes in lower zones with Larrea, or in higher zones with P. ponderosa; 600–2800 m; Ariz., Colo., Kans., Nebr., N.Mex., Okla., S.Dak., Tex., Wyo.; Mexico (Nuevo León).

Oenothera lavandulifolia is known from southern Fall River County, South Dakota, southeastern Wyoming, and far western Nebraska, through western Kansas, Colorado, eastern and southern Utah, northwestern Oklahoma, and the Texas Panhandle to trans-Pecos Texas, central New Mexico, northern and central Arizona, and eastern Nevada. It also occurs in Nuevo León, Mexico, and may be more widespread in northern Mexico. H. F. Towner (1977) found that O. lavandulifolia is self-incompatible and vespertine.