Description of Oenothera sect. Hartmannia:
Distribution: Section Hartmannia consists of five species, mostly diploid (n = 7), but in O. speciosa also n = 14 and 21. Most of the species occur in an area from Arizona and Texas south to Mexico, but O. speciosa extends to the Central Plains in the United States, and O. rosea also ranges farther to Central America, the Caribbean (Hispaniola, Jamaica, Bermuda), and northern South America to central Chile. Oenothera rosea is widely naturalized worldwide in tropical and subtropical areas. Species of sect. Hartmannia occur from near sea level to over 4,000 m elevation in South America. Four species form bivalents in meiosis, and O. rosea forms (14 and is a PTH species. Oenothera speciosa has mostly diploid (n = 7) populations with vespertine or diurnal white flowers in the northern part of its range; many of those from central Texas southward are morning-opening, pink-flowered, and mostly tetraploid (n = 14) or hexaploid (n = 21).
Habit: Perennial herbs from a taproot, sometimes with a thick somewhat woody caudex, and at least O. deserticola and O. speciosa producing new rosettes from rhizomes; stems several or sometimes more, decumbent or ascending, branched or occasionally simple.
Leaves: Leaves in a basal rosette and cauline, the cauline leaf blades 1-7(-10) cm long, elliptic to elliptic-oblanceolate or ovate, sometimes lanceolate, subserrate to weakly sinuate-toothed or occasionally sinuate-pinnatifid.
Flowers: Buds erect (or nodding on reflexed stem in O. speciosa), terete in cross section, free tips absent or minute (up to 4 mm long O. speciosa), floral tube 5-20 (-25) mm long, flaring slightly at apex, sepals splitting along one suture, remaining coherent and reflexed as a unit at anthesis or rarely separating in pairs, petals rose-purple, rarely pink or white, fading darker.
Fruit: Capsule with proximal part sterile, hollow and cylindrical, usually tapering to the base, the body clavate to narrowly ellipsoid, the valves angled or rarely with a narrow wing up to 0.5 mm wide and the upper part the face of each valve with a rib (prominent in O. speciosa), apex attenuate to a sterile beak.
Seeds: Seeds clustered in each locule, narrowly obovoid to occasionally fusiform, the surface glossy, appearing granular but minutely papillose under magnification.
Chromosomes: Chromosome numbers: n = 7 (in O. rosea (14), 14, 21; x = 7.