Herbs perennial, rarely annual, sometimes suffrutescent, caulescent; from a stout to slender taproot. Stems decumbent to ascending or erect, branched or unbranched, epidermis gray to brown, ± exfoliating. Leaves cauline, 0.3–9 cm, fascicles of small leaves often present in larger leaf axils; blade margins entire or subentire, serrate, or serrulate, sometimes spinulose. Inflorescences solitary flowers in axils of distal leaves. Flowers opening near sunset or sunrise, sometimes in afternoon, usually with a sweet scent; buds erect, terete or quadrangular, with free tips; floral tube 2–60(–70) mm; sepals flat or with keeled midribs, reflexed individually; petals yellow, usually fading dark yellow, orange, pale pink, or pale purple, suborbiculate to rhombic or obcordate; stigma usually yellow to yellow-green, blue-black in O. capillifolia subsp. capillifolia, peltate, discoid to quadrangular, sometimes shallowly 4-lobed. Capsules woody and hard to thin and ± papery, straight, cylindrical to obtusely 4-angled, often tapering at each end, dehiscent 1/2 to throughout their length; sessile. Seeds usually numerous, in 2 rows per locule, usually obovoid and somewhat angled, rarely oblanceoloid, surface smooth. 2n = 14 (28).

Distribution

w, c North America, Mexico.

Discussion

Species 7 (7 in the flora).

Section Calylophus consists of 7 species (13 taxa) classified in two subsections distributed throughout the Great Plains to Arizona and south to central Mexico with a center of diversity in Texas (H. F. Towner 1977). P. H. Raven (1964) separated Calylophus from Oenothera as treated by P. A. Munz (1965) based on its peltate stigma and unusual sporogenous tissue (Towner). The peltate stigma can now be more properly interpreted as a variation from the typical Oenothera stigma, with the indusium enlarged and the lobes reduced (W. L. Wagner et al. 2007). Molecular studies (R. A. Levin et al. 2004) strongly support both the inclusion of Calylophus within Oenothera and the monophyly of the section by inclusion of a species from each of the subsections. Subsequent detailed analyses (B. Cooper, unpubl.) indicate that subsect. Salpingia is not monophyletic with subsect. Calylophus nested within it, indicating that subsections may not be justifiable as currently defined. All species, except O. serrulata, are self-incompatible and outcrossing; flowers diurnal to vespertine, opening in the early morning or from midafternoon to near sunset, wilting in one and one-half to two days; those species with diurnal flowers are pollinated by bees [especially Halictidae (halictids) and Anthophoridae (anthophorids), often oligolectic species], those with larger vespertine flowers are pollinated by hawkmoths (Towner). The self-compatible O. serrulata is autogamous and a PTH species. Recent work (M. Moore, pers. comm.) suggests that there is additional edaphic endemism within sect. Calylophus, which is being investigated using morphology and molecular analyses (B. Cooper, unpubl.), and will likely result in detection of previously unknown species in the section.

Meriolix Rafinesque ex Endlicher 1840 is a superfluous name that pertains here.

Selected References

None.

Lower Taxa

Oenothera subsect. Calylophus, Oenothera subsect. Salpingia

Key

1	Sepals with conspicuously keeled midribs; stamens in 2 unequal series, antisepalous filaments 2 times as long as antipetalous filaments 17b.	Oenothera subsect. Calylophus
1	Sepals without keeled midribs; stamens in subequal series 17b.	Oenothera subsect. Salpingia