Oenothera deltoides var. cineracea (Jepson) Munz; O. kleinii W. L. Wagner & S. W. Mill; O. trichocalyx Nuttall var. cineracea Jepson

Herbs annual, strigillose, sometimes also villous; from a taproot. Stems: central stem erect, usually thickened, with several leafy, ascending, slender branches from near base, encircling stems in older plants, 20–60(–100) cm. Leaves basal and cauline; blade rhombic-lanceolate, becoming oblanceolate to lanceolate distally, margins usually coarsely sinuate-dentate to subentire, rarely pinnatifid. Flowers: buds weakly quadrangular, with free tips 0–1.5 mm; sepals 20–35 mm; petals 18–44 mm. Capsules 40–80 × 2–3.5 mm. 2n = 14.

Flowering (Mar–)Jun–Jul(–Sep). Sandy places, dunes, Mojave and Sonoran deserts; -50–1300 m; Ariz., Calif., Nev.; Mexico (Baja California, Sonora).

W. M. Klein (1964) determined most populations of subsp. deltoides that were studied to be self-incompatible, but found a few in Riverside County, California, to be self-compatible. Oenothera kleinii was described from a single, small roadside population near Wolf Creek Pass in Colorado. Subsequent study and discussion with W. A. Weber suggested that this pop­ulation was not native to the location, but grew there accidently; it has not been collected again in Colorado. Further study of morphological diversity of O. deltoides has shown that the distinguishing characters mentioned when O. kleinii was described, such as longer hairs and larger capsules and seeds, do in fact occur in plants within the natural range of O. deltoides.