Gaura calcicola P. H. Raven & D. P. Gregory, Mem. Torrey Bot. Club 23(1): 40, figs. 8, 43. 1973

Herbs perennial, clumped, usually sparsely strigillose, rarely glabrate or sparsely villous, hairs erect, sometimes sparsely glandular puberulent distally; from twisted, woody rootstock. Stems erect, branched below and just above ground, branched also proximal to inflorescences, (40–)60–250 cm. Leaves in a basal rosette and cauline, basal 3–13 × 0.6–2.5 cm, blade spatulate to oblanceo­late, cauline (1–)2.5–12 × 0.1–1 cm, blade linear to narrowly oblanceolate, margins slightly to conspicuously sinuate-dentate. Inflorescences slender. Flowers 4-merous, zygomorphic, opening near sunset; floral tube 3–9 mm; sepals 6–12 mm; petals white, fading dark pink to red, slightly unequal, elliptic-obovate, 7–11 mm; stamens presented in lower 1/2 of flower, filaments 3–7 mm, anthers 2.5–5 mm, pollen 90–100% fertile; style 9.5–19 mm, stigma exserted beyond anthers at anthesis. Capsules lanceoloid to narrowly ovoid, narrowly 4-winged, 7–12 × 1.5–2.5 mm, tapered to a sterile stipe 2–5 mm. Seeds (2 or)3 or 4(or 5), light brown or reddish brown, 1.5–2.5 × 0.8–1.3 mm. 2n = 14.

Flowering Apr–May. Dry limestone, gypsum, or caliche soil, slopes; 400–1800(–2100) m; Tex.; Mexico (Coahuila, Durango, Nuevo León, Tamaulipas).

Oenothera calcicola occurs at mostly higher elevations and more montane areas than other species of subsect. Stipogaura, from the southern Trans-Pecos and Edwards Plateau regions of Texas southward into northern Mexico. P. H. Raven and D. P. Gregory (1972[1973]) determined O. calcicola to be self-incompatible. It is known to form hybrids with O. suffrutescens.