Herbs annual or perennial, glabrous, strigillose and/or vil­lous, sometimes more villous distally, especially on flower parts; from a taproot, some­times lateral roots producing adventitious shoots. Stems erect or ascending, single to several from base, unbranched or many-branched throughout, 10–50 (–70) cm. Leaves cauline, rosette usually weakly developed or absent, at least during flowering, sometimes well developed, 1–5 (–7.8) × 0.3–1 (–1.5) cm; petiole 0–2 (–4.5) cm; blade lanceolate, oblong, linear-lanceolate, or ovate, margins subentire or remotely denticulate, deeply sinuate-dentate, or pinnatifid, sometimes repand. Flowers 1–several opening per day near sunset; buds nodding, weakly quadrangular, with free tips 0–2 mm; floral-tube 15–40 mm; sepals 10–30 mm, not spotted; petals white, fading pink to deep pink, broadly obovate or obcordate, (10–) 15–25 (–40) mm; filaments 9–15 mm, anthers 3–10 mm; style 25–55 mm, stigma exserted beyond anthers at anthesis. Capsules spreading to reflexed, straight to curved or contorted, cylindrical, obtusely 4-angled, tapering slightly from base to apex, 15–60 × 1.5–2.5 mm; sessile. Seeds numerous, in 1 row per locule, brownish with dark spots or black, narrowly obovoid, 1.5–2.2 mm.

Distribution

w, c North America, n Mexico

Discussion

Subspecies 4 (4 in the flora).

Oenothera pallida is a poorly understood species currently subdivided into four subspecies (W. L. Wagner et al. 2007) that differ largely in aspect, leaf division, capsule configuration, and pubescence. The variation pattern is rather complex with almost no diagnostic character uniformly distinguishing any one of the subspecies. Instead, each of the subspecies, which are mostly geographically separated although there is some level of overlap, have diagnostic suites of characters that maintain their linkage some of the time, but break down across the geographic area of each so that no single character uniquely identifies it. Each subspecies is characterized by leaf, pubescence, and, often, habit features. The issues with the integrity and intergrada­tions of the subspecies are discussed below.

Oenothera pallida has been determined to be self-incompatible (W. L. Wagner et al. 2007), but K. E. Theiss et al. (2010) determined that although most populations of subsp. pallida are self-incompatible, one near Salt Lake City is self-compatible.

Selected References

None.

Lower Taxa

Oenothera pallida subsp. latifolia, Oenothera pallida subsp. pallida, Oenothera pallida subsp. runcinata, Oenothera pallida subsp. trichocalyx

Key

1	Herbs annual, sometimes perennial from a taproot, when perennial, sometimes with lateral roots producing adventitious shoots, strigillose throughout and villous distally, especially on flower parts.	Oenothera pallida subsp. trichocalyx
1	Herbs perennial from a taproot and with lateral roots producing adventitious shoots, glabrous, strigillose, or sparsely villous.	> 2
2	Plants glabrous, sometimes strigillose, rarely sparsely villous; leaf blade margins usually subentire or remotely denticulate, rarely pinnatifid; capsules usually contorted to curved.	Oenothera pallida subsp. pallida
2	Plants usually strigillose, rarely villous or glabrous; leaf blade margins shallowly sinuate-dentate or denticulate, or deeply sinuate-dentate to pinnatifid, rarely only dentate; capsules usually straight or curved, sometimes contorted.	> 3
3	Leaf blades (0.4–)0.7–1.5 cm wide, margins shallowly sinuate-dentate or denticulate.	Oenothera pallida subsp. latifolia
3	Leaf blades 0.4–1(–1.5) cm wide, margins usually deeply sinuate-dentate to pinnatifid, rarely dentate only.	Oenothera pallida subsp. runcinata