Herbs winter-annual or perennial, caulescent; from a taproot or lateral roots producing adventitious shoots. Stems 1–several arising from rosette, decumbent to ascending or erect, unbranched or with short, lateral branches, epidermis white or pink, not exfoliating. Leaves in a basal rosette and cauline, cauline 1–10 cm; blade margins entire, with few coarse teeth, lobed or pinnatifid. 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, weakly quadrangular, without free tips; floral-tube 10–30 mm; sepals separating in pairs or individually; petals white, fading pink, obcordate to obovate; stigma deeply divided into 4 linear lobes. Capsules straight or sometimes curved upward, cylindrical or fusiform, obtusely 4-angled, tapering toward base and apex, dehiscent 1/2 their length; sessile. Seeds numerous, in 2 rows per locule, ellipsoid to subglobose, surface regularly pitted, pits in longitudinal lines. 2n = 14, 28.

Distribution

w United States, n Mexico

Discussion

Species 2 (2 in the flora).

Section Kleinia consists of two species of usually open sandy or rocky sites from the Chihuahuan, Sonoran, and southern portions of the Great Basin deserts to the Great Plains, from southern Utah to southeastern Montana and western North Dakota, south to northern Mexico (Chihuahua and Sonora) at 1000 to 3000 m; Oenothera coronopifolia generally occurs at higher elevations than O. albicaulis. As summarized by W. L. Wagner et al. (2007; see also K. E. Theiss et al. 2010), O. albicaulis is diploid (2n = 14) and O. coronopifolia has both diploid and tetraploid (2n = 14, 28) populations. Both species are self-incompatible and the vespertine flowers are pollinated by hawkmoths, especially Hyles and Manduca. P. H. Raven (1979) reported that O. coronopifolia had both self-incompatible and self-compatible populations. Theiss et al. found only self-incompatible plants in one population examined.

Section Kleinia is included within a strongly supported clade with members of sect. Anogra in recent molecular studies (R. A. Levin et al. 2004; M. E. K. Evans et al. 2005, 2009); placement of the subclade of the two sect. Kleinia species within the overall clade is not strongly resolved. For the present, the classification, based on morphology, is maintained until further resolution can be obtained. Section Kleinia can be distinguished by a number of morphological characteristics, including capsule shape, seeds in two rows per locule, and seeds with anatomy similar to that found in sect. Oenothera subsect. Raimannia but unlike that in sect. Anogra (W. L. Wagner et al. 2007; H. Tobe et al. 1987). P. A. Munz (1965) described sect. Kleinia as part of his subg. Raimannia, thus including these two white-flowered species in an otherwise yellow-flowered group because of similarities of the capsules and seeds. This group has been viewed as intermediate between sect. Oenothera subsect. Raimannia and sect. Anogra (Wagner et al.). Although both sects. Anogra and Kleinia have morphological synapomorphies that define them, a section combining them would be united by nodding buds and white petals; both characters are not unique morphological synapomorphies.

Selected References

None.

Lower Taxa

Oenothera albicaulis, Oenothera coronopifolia

Key

1	Herbs annual, from a taproot; floral tube mouth glabrous.	Oenothera albicaulis
1	Herbs perennial, lateral roots producing adventitious shoots; floral tube mouth conspicuously pubescent.	Oenothera coronopifolia

"/2" is not declared as a valid unit of measurement for this property.