Herbs annual, biennial, or clumped perennial (O. lindheimeri); from robust taproot. Stems single or several from base, sometimes branched distally. Inflorescences erect. Flowers (3 or)4-merous, strongly zygomorphic, opening near sunset or sunrise; floral tube 3–14(–20) mm; petals white, slightly unequal; filaments with basal scales. Capsules erect, ellipsoid, ovoid, or narrowly obovoid, sharply (3- or)4-angled or narrowly (3- or)4-winged, abruptly constricted or tapered to base; sessile. 2n = 14.

Distribution

North America, Mexico, Central America (Guatemala).

Discussion

Species 13 (12 in the flora).

Subsection Gaura is the largest subsection of sect. Gaura. W. L. Wagner et al. (2007) combined the two sections (Gaura and Pterogaura) recognized by P. H. Raven and D. P. Gregory (1972[1973]) into a single subsection based on recent molecular studies by G. D. Hoggard et al. (2004) and R. A. Levin et al. (2004). The two groups are quite similar morphologically, differing primarily in the shape of the base of the fruit (abruptly constricted versus tapering). Subsequent analyses by Wagner et al. (2013; K. Krakos, unpubl.), which sampled all 13 taxa of subsect. Gaura, showed that none of the three species (O. coloradensis, O. hexandra, and O. suffulta) subdivided into two subspecies each by Raven and Gregory and maintained in Oenothera by Wagner et al. were monophyletic, and these taxa were recently recognized as six species with the additional ones being O. dodgeniana, O. nealleyi, and O. podocarpa (Wagner et al. 2013). A majority of the species of subsect. Gaura occur in the central and eastern United States, but the subsection extends west to Colorado and Wyoming (O. coloradensis), New Mexico (O. dodgeniana, O. nealleyi, O. podocarpa), and Arizona (O. podocarpa), south­ward into Mexico in the Sierra Madre Occidental and the Trans-Volcanic Belt, to Guatemala (O. hexandra). Five species (O. demareei, O. filiformis, O. lindheimeri, O. nealleyi, and O. suffulta) are self-incompatible with the other eight species self-compatible and exhibiting variable degrees of autogamy. Two of the self-compatible and autogamous species, O. gaura and O. triangulata, are PTH species and form a ring of 14 chromosomes in meiosis (Raven and Gregory).

Pleurandra Rafinesque (1817), not Pleurandra Labillardière (1806), is an illegitimate homonym that pertains here.

Selected References

None.

Lower Taxa

Oenothera coloradensis, Oenothera demareei, Oenothera dodgeniana, Oenothera filiformis, Oenothera gaura, Oenothera lindheimeri, Oenothera nealleyi, Oenothera patriciae, Oenothera podocarpa, Oenothera simulans, Oenothera suffulta, Oenothera triangulata

Key

1	Flowers 3- or, rarely, 4-merous; capsules 3(or 4)-winged or 3(or 4)-angled.	> 2
2	Plants usually unbranched proximally, 60–180 cm; capsules narrowly ellipsoid or ovoid.	Oenothera simulans
2	Plants usually branched proximally, 15–65(–85) cm; capsules ellipsoid or narrowly obovoid.	> 3
3	Sepals 10–15 mm; pollen 90–100% fertile.	Oenothera patriciae
3	Sepals 4.5–6 mm; pollen 35–65% fertile.	Oenothera triangulata
1	Flowers 4-merous; capsules 4-winged or 4-angled.	> 4
4	Flowers opening at sunrise; herbs perennial (clumped), usually branched from base, villous throughout, usually also glandular puberulent in distal parts.	Oenothera lindheimeri
4	Flowers usually opening at sunset, rarely at sunrise (O. demareei); herbs usually annual or biennial, rarely monocarpic perennial, branched or unbranched, villous, strigillose, or short-hirtellous throughout, distal parts usually glandular puberulent, short-hirtellous, strigillose, or glabrate, sometimes villous.	> 5
5	Capsules winged, furrowed between wings; stems 15–120 cm.	> 6
6	Sepals 6–15 mm; floral tubes 6–12 mm.	> 7
7	Sepals 6–12 mm; plants glabrate, glandular puberulent, and/or sparsely strigillose distally.	Oenothera podocarpa
7	Sepals 10–15 mm; plants usually glabrate, sometimes strigillose distally.	Oenothera patriciae
6	Sepals 11–21 mm; floral tubes 6.5–20 mm.	> 8
8	Plants glabrous distally, except sometimes proximal part of inflorescence, especially bracts, sparsely villous; capsules with stipes 0–1 mm.	Oenothera suffulta
8	Plants glandular puberulent distally; capsules with stipes 0.2–2 mm.	Oenothera nealleyi
5	Capsules angled, not winged; stems 50–400 cm.	> 9
9	Sepals 2.5–8 mm; stems usually unbranched, sometimes with several branches from base.	Oenothera simulans
9	Sepals (5–)9–20 mm; stems usually branched from base upwards.	> 10
10	Flowers opening at sunrise; plants exclusively strigillose throughout.	Oenothera demareei
10	Flowers opening at sunset; plants with some combination of villous, glandular puberulent, short-hirtellous, or strigillose.	> 11
11	Anthers: pollen 35–65% fertile; plants villous and glandular puberulent, rarely short-hirtellous, not strigillose.	Oenothera gaura
11	Anthers: pollen 90–100% fertile; plants strigillose, villous, short-hirtellous, glabrate, or glandular puberulent distally.	> 12
12	Herbs annual; capsules 4.5–7 mm.	Oenothera filiformis
12	Herbs biennial or monocarpic perennial; capsules 6–11 mm.	> 13
13	Herbs monocarpic perennial, strigillose proximally, becoming short- hirtellous and strigillose distally.	Oenothera coloradensis
13	Herbs biennial, villous and strigillose proximally, becoming also glandular puberulent distally and also sparsely villous.	Oenothera dodgeniana