Herbs perennial, sometimes suffrutescent, clumped or spreading by rhizomes; from woody, often twisted roots. Stems ascending to erect, several from near base, usually also branched from shortened internodes (forming a whorl of branches just proximal to inflorescence). Inflorescences wandlike, erect. Flowers 4-merous, strongly zygomorphic, opening near sunset; floral tube 1.5–9 mm; petals white, slightly unequal; filaments with basal scales. Capsules reflexed, lanceoloid to ovoid, narrowly 4-winged or, sometimes, 4-angled, abruptly constricted or tapered to a slender, sterile stipe; sessile. 2n = 14, 28.

Distribution

sw, e United States, ne Mexico.

Discussion

Species 5 (5 in the flora).

Species of subsect. Stipogaura are distributed in sandy or rocky open sites from eastern New Mexico, western Texas, and northeastern Mexico to the eastern United States in southern Indiana, Kentucky, and South Carolina, with partially overlapping ranges, replacing one another geographically (P. H. Raven and D. P. Gregory 1972[1973]). All of the species of the section are self-incompatible, the flowers vespertine, pollinated by a wide variety of insects (Raven and Gregory); one species (Oenothera cinerea) is visited by at least 32 species of insect pollen carriers, the most important of which are antlions in the genus Scotoleon, two species of noctuid moths, and two species of the nocturnal, oligolectic halictid bee Sphecodogastra (R. R. Clinebell et al. 2004).

Selected References

None.

Lower Taxa

Oenothera calcicola, Oenothera cinerea, Oenothera filipes, Oenothera mckelveyae, Oenothera sinuosa

Key

1	Herbs suffrutescent, densely soft-villous, hairs mostly appressed, also strigillose and, rarely, glandular puberulent, plant parts grayish green.	Oenothera cinerea
1	Herbs not suffrutescent, strigillose and/or villous with spreading hairs, sometimes also glandular puberulent, plant parts green.	> 2
2	Cauline leaves 1–3(–7) cm, blade margins conspicuously sinuate-dentate; stems ascending, 30–70(–120) cm; plants strigillose and villous, hairs 2–4 mm, sometimes glabrate or glandular puberulent distally.	Oenothera mckelveyae
2	Cauline leaves (1–)2.5–12 cm, blade margins subentire or sinuate-dentate; stems erect, 40–250(–300) cm; plants glabrous or strigillose, sometimes also sparsely villous, hairs 1–2 mm, sometimes glandular puberulent distally.	> 3
3	Herbs rhizomatous perennials (usually forming extensive colonies), usually glabrous, sometimes strigillose.	Oenothera sinuosa
3	Herbs clumped perennials, usually sparsely to densely strigillose or glabrous, sometimes glabrate or sparsely villous, sometimes sparsely glandular puberulent distally.	> 4
4	Stamens presented at anthesis in lower 1/2 of flower; capsules lanceoloid to narrowly ovoid; plants usually sparsely strigillose, sometimes sparsely glandular puberulent distally, rarely glabrate, or sparsely villous.	Oenothera calcicola
4	Stamens presented at anthesis evenly around flower parts; capsules ovoid; plants sparsely to densely strigillose, inflorescence usually glabrous or glandular puberulent, sometimes proximalmost parts villous.	Oenothera filipes