Description of Oenothera sect. eremia:
Distribution: Section Eremia consists of a single species, O. primiveris, which occurs in the Chihuahuan, Mojave, and Sonoran deserts in sandy soils on flats, low hills and margins of sand dunes, or along arroyos and roadsides, from 30 to 1,600 m elevation or rarely slightly higher. The range extends from southeastern California across southern Nevada to southern Utah (Emery, Kane, and Washington counties), northwestern Mohave Co., Arizona, and south of the Mogollon Plateau to southern New Mexico, western Texas, and in Mexico to Chihuahua, Sonora, and northern Baja California, Mexico.
Habit: Winter annual herbs, from a weakly fleshy taproot; stems absent or occasionally ascending to erect, densely leafy.
Leaves: Leaves in a basal rosette, sometimes also cauline, (1.5-)6-15 (-28) cm long, sinuate-dentate to subentire, tapering to a winged petiole.
Flowers: Flowers axillary, congested on relatively short axes, apex of bud curved downward by the recurved floral tube, becoming erect before anthesis, quadrangular in cross section, without free sepal tips, floral tube 20-72 mm long, flaring somewhat at the mouth, sepals separating individually or in pairs, petals deep yellow, fading reddish orange to purple, drying purple.
Fruit: Capsule lanceoloid to ovoid, sigmoid or curved to nearly straight, quadrangular in cross section, the angle acute, asymmetrical at the base, dehiscing 1/4 to 2/3 of the length, sessile.
Seeds: Seeds 30-160, in 2 rows per locule, obovoid to oblanceloid; the testa much thickened above the raphe and at the distal end into a U-shaped structure, the thickened area with a central cavity that externally appears as a pore at the distal end and a groove along the raphial face; the surface papillose, but coarsely rugose on the distal half of the abaxial side, the papillae apically depressed.
Chromosomes: Chromosome number: n = 7.