Oenothera sect. Oenothera

Herbs annual, biennial, or perennial, caulescent; from a usually large taproot, sometimes developing adventitious shoots from lateral roots producing a fibrous root system. Stems erect to ascending or decumbent, branched or unbranched. Leaves in a basal rosette and cauline, cauline (1–)3–25 cm; blade margins pinnately lobed to sinuate-dentate, serrate to dentate or subentire. Inflorescences solitary flowers in axils of distal leaves, usually forming a dense or lax spike. Flowers opening near sunset, with a sweet scent or nearly unscented; buds erect or recurved, terete or weakly quadrangular, with free tips; floral tube 12–165(–190) mm; sepals separating in pairs and reflexed, or splitting along only 1 suture and reflexed to one side as a unit, or separate and reflexed individually; petals yellow, usually fading orange, reddish orange, yellow, or yellowish white, usually obcordate to obovate, sometimes rhombic, elliptic, or rhombic-ovate; stigma deeply divided into 4 linear lobes. Capsules straight, curved, or somewhat sigmoid, becoming somewhat woody in age, cylindrical to narrowly lanceoloid or ovoid, terete to weakly 4-angled dehiscent nearly throughout their length; sessile. Seeds numerous, in (1 or) 2 rows per locule, prismatic and angled, narrowly to broadly ellipsoid to subglobose, rarely obovoid and obtusely angled, surface reticulate and regularly or irregularly pitted, rarely flat. 2n = 14.

Distribution

North America, Mexico, West Indies (Cuba), Bermuda, Central America, South America, introduced widely in temperate areas of the world.

Discussion

Species 68 (26 in the flora).

Section Oenothera is the largest section in the genus, consisting of 68 species (79 taxa) divided into six subsections, one of which is further divided into three series. Section Oenothera has a wide geographic distribution from Canada south to Panama and throughout temperate South America, essentially encompassing the full natural distribution of the genus, although there is very sparse representation (only O. elata) from central Mexico south to Panama. Species of this section occur in a variety of habitats, often disturbed ones, from sea level to 5000 m. Most of the species are self-compatible, but with a few self-incompatible taxa and individual populations of others (W. Dietrich et al. 1997; W. L. Wagner et al. 2007). The flowers are vespertine, fading the following morning, and are pollinated by hawkmoths (in O. versicolor Lehmann perhaps by hummingbirds), or autogamous. In sect. Oenothera, as in several other sections of the genus, the diploid, bivalent-forming, usually outcrossing, species often have relatively narrow geographic and ecological ranges, whereas closely related PTH species derived from them are usually autogamous and have much wider ranges. There are 37 PTH species in sect. Oenothera, which includes the majority of species of angiosperms with this anomalous genetic system.

Selected References

None.

Lower Taxa

Oenothera subsect. Candela, Oenothera subsect. Emersonia, Oenothera subsect. Munzia, Oenothera subsect. Nutantigemma, Oenothera subsect. Oenothera, Oenothera subsect. Raimannia

Key

1	Floral tubes 100–165(–190) mm; herbs perennial 17p.	Oenothera subsect. Emersonia
1	Floral tubes (5–)12–50(–160) mm; herbs annual, biennial, or short-lived perennial.	> 2
2	Seeds prismatic and angled, surface irregularly pitted 17p.	Oenothera subsect. Oenothera
2	Seeds ellipsoid to subglobose, not angled, surface regularly pitted.	> 3
3	Young flower buds nodding by recurved floral tube 17p.	Oenothera subsect. Nutantigemma
3	Young flower buds with floral tube curved upward or straight.	> 4
4	Petals rhombic to elliptic or rhombic-ovate 17p.	Oenothera subsect. Candela
4	Petals shallowly or deeply obcordate.	> 5
5	Young flower buds with floral tube curved upward 17p.	Oenothera subsect. Raimannia
5	Young flower buds with floral tube straight 17p.	Oenothera subsect. Munzia