Herbs winter-annual or perennial, caulescent; from a taproot, sometimes lateral roots pro­ducing adventitious shoots. Stems decumbent to ascending or erect, unbranched or with short, lateral branches, epidermis white or pink, exfoliating proximally. Leaves basal and cauline, sometimes forming conspicuous basal rosette, sometimes this weakly developed or absent (at least during flowering), 1–13(–26) cm; blade margins sinuate-dentate to pinnatifid, denticulate, subentire, or entire. Inflorescences solitary flowers in axils of distal leaves. Flowers opening near sunset, with a sweet scent or nearly unscented; buds nodding by recurved floral tube, usually sharply or bluntly quadrangular in cross section (sometimes fluted in distal 1/2 in O. deltoides), without free tips or free tips short (sometimes to 9 mm in O. deltoides); floral tube 15–40(–50) mm; sepals separatingin pairs or individually; petals white, fading pink, obcordate to obovate; stigma deeply divided into 4 linear lobes. Capsules straight, curved upward, spreading, or contorted, sometimes woody in age, cylindrical, obtusely 4-angled, gradually tapering from base to apex, dehiscent 1/2 to nearly throughout; sessile. Seeds numerous, in 1 row per locule, obovoid, surface minutely alveolate, but appearing smooth. 2n = 14, 28.

Distribution

w, c North America, n Mexico.

Discussion

Species 8 (7 in the flora).

Section Anogra consists of eight species (17 taxa) native to western North America including Mexico, found usually in dry, sandy soil in a wide variety of habitats in the Chihuahuan, Great Basin, Mojave, and Sonoran deserts, to grasslands and open sites in montane forest, -50 to 3300 m. Only one species, Oenothera wigginsii Klein, occurs entirely outside the United States, while four others occur within the flora area but extend into northern Mexico. Section Anogra is included within a strongly supported clade with the two species of sect. Kleinia in recent molecular studies (R. A. Levin et al. 2004; M. E. K. Evans et al. 2005, 2009). The support levels for the topology within this clade are generally very weak, with only a few taxa grouping into moderately to strongly supported groups (for example, members of O. pallida complex, O. deltoides + O. wigginsii, O. avita + O. arizonica and O. neomexicana).

Species of sect. Anogra have vespertine flowers that are outcrossed and pollinated by hawkmoths or have flowers that are partly autogamous (D. P. Gregory 1964; W. M. Klein 1964, 1970). In Oenothera deltoides the capsule valves split open widely and disperse seeds, while the entire plant forms a so-called tumbleweed. Other species in the section appear to have more passive seed dispersal; the capsules dehisce while the plant remains rooted. The basal rosette may not be evident at time of flowering or not developed. When this is the case, or when the dimensions of the basal leaves are very similar to the cauline ones, only one range for leaf dimensions is given.

Selected References

None.

Lower Taxa

Oenothera arizonica, Oenothera avita, Oenothera deltoides, Oenothera engelmannii, Oenothera neomexicana, Oenothera nuttallii, Oenothera pallida

Key

1	Herbs winter-annual or short-lived perennial from a taproot.	> 2
1	Herbs perennial, from a taproot, also with lateral roots producing adventitious shoots or with long, fleshy roots.	> 5
2	Sepals conspicuously maroon-spotted.	Oenothera arizonica
2	Sepals without maroon spots.	> 3
3	Plants villous throughout, also strigillose on leaves and distal parts; leaf blade margins coarsely repand-dentate or -pinnatifid.	Oenothera engelmannii
3	Plants villous, strigillose, or glabrous, sometimes more densely villous or strigillose distally; leaf blade margins subentire to sinuate-dentate or remotely denticulate, sometimes pinnatifid.	> 4
4	Capsules 2.5–5 mm diam.; sepals (13–)15–35 mm.	Oenothera deltoides
4	Capsules 1.5–2.5 mm diam.; sepals 10–18 mm.	Oenothera pallida
5	Buds fluted in distal 1/2, with free tips 1–9 mm; plants from relatively long, fleshy roots.	Oenothera deltoides
5	Buds quadrangular in distal 1/2, with free tips 0–4 mm; plants from a taproot and with lateral roots producing adventitious shoots.	> 6
6	Plants glabrous, sometimes strigillose on leaves and/or glandular puberulent distally, at least on floral tube; leaf blades 0.3–0.6(–1) cm wide, narrowly oblong to oblong- lanceolate, margins usually entire.	Oenothera nuttallii
6	Plants villous, strigillose, glabrate, or glabrous, not glandular puberulent; leaf blades (0.3–)1–2.5 cm wide, usually ovate, oblong to lanceolate or linear-lanceolate, oblanceolate, or spatulate, rarely rhombic-ovate, margins usually sinuate-dentate to pinnatifid or subentire, rarely entire.	> 7
7	Capsules erect or strongly ascending.	Oenothera neomexicana
7	Capsules spreading to reflexed.	> 8
8	Capsules 2–3.5 mm diam.; stems decumbent or ascending.	Oenothera avita
8	Capsules 1.5–2.5 mm diam.; stems erect or ascending.	Oenothera pallida