Oenothera clutei A. Nelson; O. longissima subsp. clutei (A. Nelson) Munz; O. longissima var. clutei (A. Nelson) Munz

Herbs biennial or short-lived perennial, sparsely strigillose, sometimes also villous and with pustulate hairs near inflorescence, sometimes also glandular puberulent. Stems erect, usually flushed with red proximally or sometimes green, unbranched or with branches obliquely arising from base, secondary branches arising from main stem, 60–300 cm. Leaves in a basal rosette and cauline, basal 9–40 × 1.4–5 cm, cauline 5–22 × 0.8–2.5 cm; blade dull green, flat, narrowly oblanceolate, oblanceolate to narrowly elliptic, or narrowly lanceolate, margins bluntly dentate or subentire, teeth widely spaced; bracts persistent. Inflorescences open, erect, unbranched. Flowers opening near sunset; buds erect, 5–9 mm diam., with free tips terminal, erect, 2–6 mm; floral tube deciduous after anthesis, 60–135 mm; sepals yellowish green, flushed with some red or red to dark red throughout, 25–55 mm; petals yellow to pale yellow, fading orange or pale yellow, very broadly obcordate, 28–65 mm; filaments 20–40 mm, anthers 14–20 mm, pollen 90–100% fertile; style 90–180 mm, stigma exserted beyond anthers at anthesis. Capsules erect or slightly spreading, dull green or gray-green when dry, narrowly lanceo­loid, 25–55 × 4–9 mm, free tips of valves 1–2(–3) mm. Seeds 1–1.9 × 0.6–1.2 mm. 2n = 14.

Flowering Jul–Sep(–Oct). Seasonally moist sites, sandy or sandy-loam soil, sites with high alkalinity or associated with limestone, along desert washes, streams, seeps, roadsides; 800–2800 m; Ariz., Calif., Colo., Nev., N.Mex., Utah.

Oenothera longissima has plastome I and a AA genome composition.

Oenothera longissima is known from northern and western Arizona, Inyo, Los Angeles, and San Bernardino counties in California, Delta and Montezuma counties in Colorado, eastern Nevada, San Juan County in New Mexico, and southern Utah.