16. Oenothera speciosa Nuttall, J. Acad. Nat. Sci. Philadelphia. 2: 119. 1821.
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Hartmannia berlandieri (Spach) Rose; H. reverchonii Rose; Oenothera berlandieri (Spach) Spach ex D. Dietrich; O. delessertiana Steudel; O. hirsuta (Spach) D. Dietrich; O. obtusifolia (Spach) D. Dietrich; O. shimekii H. Léveillé & Guffroy; O. spachii D. Dietrich; O. speciosa var. berlandieri (Spach) Munz; O. speciosa var. childsii (L. H. Bailey) Munz; O. tetraptera Cavanilles var. childsii L. H. Bailey; Xylopleurum berlandieri Spach; X. drummondii Spach; X. hirsutum Spach; X. obtusifolium Spach;X. speciosum (Nuttall) Raimann
Herbs perennial, caulescent, glabrate to strigillose, usually also sparsely hirsute; from slender taproot and spreading by rhizomes. Stems many, erect, 4–60 cm. Leaves in a basal rosette and cauline, basal 2–9 × 0.3–3.2 cm, blade oblanceolate to obovate, margins subentire or sinuate-pinnatifid; cauline 1–10 × 0.3–3.5 cm, blade narrowly elliptic to ovate, margins subentire or serrulate to sinuate-pinnatifid. Inflorescences sharply nodding. Flowers 1–3 opening per day near sunrise in some populations, near sunset in others; buds with free tips 0–4 mm; floral tube 12–25 mm; sepals 15–50 mm; petals pink to rose, fading darker, or white, fading pink, 15–45 mm; filaments 10–22 mm, anthers 6–16 mm, pollen 85–100% fertile; style 20–55 mm, stigma exserted beyond anthers at anthesis. Capsules narrowly obovoid to narrowly rhombic-ellipsoid, angled, 10–25 × 3.5–6 mm, apex attenuate to a sterile beak, valve midrib prominent, proximal stipe cylindrical, not tapering to base, (4–)8–15 mm; sessile. Seeds narrowly obovoid, 1–1.2 × 0.5–0.6 mm. 2n = 14, 28, 42.
Flowering (Feb–)Apr–Jul(–Oct). Grasslands, glades, open woodlands, disturbed places, pastures, railroads, roadsides, loamy or sandy soil, sometimes clay; 10–900 m; Ark., Ill., Ind., Iowa, Kans., La., Mo., Nebr., N.Mex., Okla., Tex.; Mexico (Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Tamaulipas).
Oenothera speciosa is widely cultivated worldwide for its showy flowers and easy maintenance. It is not known to be definitely naturalized, but tends to persist or become adventive due to its aggressive vegetative reproduction.
