Oenothera tubicula A. Gray var. filifolia Eastwood, Proc. Calif. Acad. Sci., ser. 3, 1: 72, plate 6, fig. 1. 1897; Calylophus hartwegii (Bentham) P. H. Raven subsp. filifolius (Eastwood) Towner & P. H. Raven; C. hartwegii var. filifolius (Eastwood) Shinners; Galpinsia filifolia (Eastwood) A. Heller; O. filifolia (Eastwood) Tidestrom; O. hartwegii var. filifolia (Eastwood) Munz

Herbs glandular puberulent throughout, more densely so on distal parts, sometimes also sparsely strigillose on ovaries and leaves. Leaves 0.3–4 × 0.04–0.3(–0.4) cm, fascicles of small leaves to 1.5 cm often present in axils; blade filiform to narrowly lanceolate, base attenuate, margins entire or remotely serrulate, sometimes undulate. Flowers: buds with free tips 0.5–4 mm; floral tube 16–50 mm; sepals 7–17 mm; petals 12–23 mm; filaments 6–13 mm, anthers 6–11 mm; style 26–60 mm. 2n = 14.

Flowering May–Oct. Highly local, often abundant, almost always on semiarid gypsum flats, dunes, or outcrops, with Juniperus, Larrea, and Yucca; 600–1900 m; N.Mex., Tex.; Mexico (Chihuahua, Coahuila, Zacatecas).

Subspecies filifolia occurs in Otero and Torrance counties in southeastern New Mexico, south and east through the Trans-Pecos and southern Panhandle of Texas to Cottle County in Texas, and southward from widely scattered localities in central Chihuahua, Coahuila, and Zacatecas, Mexico.