Description of Oenothera sect. Kleinia:
Distribution: This section 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 (Sonora and Chihuahua), up to 2,800 m elevation (O. coronopifolia generally occurring at higher elevations than O. albicaulis). Oenothera albicaulis is diploid (n = 7) and O. coronopifolia has both diploid and tetraploid (n = 14) populations.
Habit: Winter annual or perennial herbs, from a taproot or lateral roots occasionally producing new shoots; stems several, arising from the rosette, unbranched or with short lateral branches, decumbent to ascending, with white or pink epidermis, not exfoliating.
Leaves: Leaves basal and cauline, 1-5 cm long, oblong-lanceolate to oblanceolate, sinuate-dentate to pinnatifid.
Flowers: Buds terete in cross section, apex of bud curved downward by the recurved floral tube, without free tips, floral tube 15-30 mm long, slightly flaring at apex, sepals separating in pairs or individually, petals white, fading pink.
Fruit: Capsule cylindrical or oblongfusiform and tapering toward apex and base, weakly 4-angled, straight or sometimes curved upward, dehiscing ca. 1/2 of the length, sessile.
Seeds: Seeds numerous, in 2 rows per locule, ellipsoid to subglobose, the testa regularly pitted, the pits in longitudinal lines.
Chromosomes: Chromosome numbers: n = 7, 14; x = 7.