Galpinsia carlsbadiana A. Nelson; Oenothera tubicula var. demissa A. Gray; O. ×serrulatoides H. Léveillé

Herbs short-lived perennial, glandular puberulent; from a stout taproot. Stems 1–many, unbranched to densely branched, decumbent to erect, 4–53 cm. Leaves 0.7–4.6 × 0.1–1.2 cm, sometimes fascicles of small leaves 0.2–1.5 cm present in non-flowering axils; petiole 0–0.2 cm; blade linear to ovate or obovate, base attenuate, margins entire, apex acute. Flowers usually several per stem opening per day near sunrise; buds with free tips 0.5–2 mm; floral tube 5–25(–33) mm, funnelform in distal 1/2 or more; sepals 3–13 mm; petals yellow, fading pale pink or pale purple, 5–20(–25) mm; filaments 1–6 mm, anthers 2–7 mm, pollen 85–100% fertile; style 9–30(–40) mm, stigma yellow, quadrangular, usually exserted beyond anthers. Capsules 8–20 × 1.5–2.5 mm, hard, promptly dehiscent throughout their length. Seeds obovoid, 1–1.4 mm. 2n = 14.

Flowering Apr–Aug. Colonial, primarily on limestone soil, in flat arid grasslands, with Larrea and Yucca; 600–1400 m; N.Mex., Tex.; Mexico (Coahuila, Nuevo León, Tamaulipas, Zacatecas).

Subspecies tubicula is known from Guadalupe County, New Mexico, south in the western side of the Pecos River drainage to western Texas, where it occurs from Culberson County east to Howard County, thence south through Brewster, Presidio, and Terrell counties, and probably most of central Coahuila, to north­ern Zacatecas, southwestern Nuevo León, and south­­western Tamaulipas.