8. Oenothera hartwegii Bentham, Pl. Hartw. 5. 1839. (as hartwegi).
[F]
Calylophus hartwegii (Bentham) P. H. Raven; Galpinsia hartwegii (Bentham) Britton; Salpingia hartwegii (Bentham) Raimann
Herbs perennial, sometimes suffrutescent, strigillose, glandular puberulent, glabrous, hirtellous, or short-pilose; from a stout taproot. Stems 1–many, erect to ascending, unbranched to densely branched, 4–60 cm. Leaves 0.3–6.5 × 0.04–1.2 cm, sometimes fascicles of small leaves 0.1–1.5 cm present in non-flowering axils; petiole 0–0.2 cm; blade elliptic, lanceolate, linear, or filiform to ovate or oblanceolate, usually not much reduced distally, proximalmost leaves sometimes obovate to spatulate, base attenuate to obtuse, truncate, or subcordate, sometimes clasping, margins entire or serrate, often undulate, apex acute. Flowers usually 1 per stem opening per day in afternoon or near sunset; buds with free tips 0.5–6 mm; floral tube 16–50(–60) mm, funnelform in distal 1/2 or less; sepals 7–28 mm; petals yellow, fading pale pinkish or pale purple, 10–35 mm; filaments 4–13 mm, anthers 5–13 mm, pollen 85–100% fertile; style 25–65(–75) mm, stigma yellow, quadrangular, usually exserted beyond anthers. Capsules 6–40 × 2–4 mm, hard, promptly dehiscent throughout their length. Seeds obovoid, 1–2.5 mm. 2n = 14, 28.
Subspecies 5 (5 in the flora): sw, c United States, n Mexico.
Oenothera hartwegii consists of five intergrading subspecies, which are generally locally common on rocky, sandy, gypsum, or limestone soil in arid to relatively mesic open areas, in southeastern Colorado, southwestern Kansas, western Oklahoma, Texas (except eastern part), New Mexico, southeastern and east-central Arizona, and in Mexico from Chihuahua, northern Coahuila, and northwestern Tamaulipas south to Aguascalientes. H. F. Towner (1977) found that O. hartwegii is self-incompatible and usually vespertine; two of the subspecies (filifolia and maccartii) open early in the afternoon and are pollinated both day and evening.
