Description of Oenothera sect. Paradoxus:
Distribution: This section consists of a single species (O. havardii), restricted to the Chihuahuan Desert from Presidio and Brewster counties, Texas, and Cochise Co., Arizona, south to Durango and Zacatecas, Mexico. It occurs in depressions, seasonally wet flats, along stream banks, and on the margins of irrigated fields, often growing among grasses, from 1,300 to 2,000 m elevation.
Habit: Perennial herbs from a taproot, spreading by adventitious shoots from lateral roots; stems branched or simple, weakly erect and becoming decumbent, forming compact to sprawling masses, often twining among vegetation, sometimes rooting at the nodes.
Leaves: Leaves usually quickly deciduous, cauline leaves linear-lanceolate, 1-5 cm long, irregularly pinnately lobed to sinuate-toothed or dentate.
Flowers: Buds erect, terete in cross section, the apex long-acuminate, often twisted, sepal tips coherent, floral tube 37-65 mm, flaring at the mouth, sepals splitting along one suture and reflexed as a unit to one side, petals lemon-yellow, fading orange-red, drying reddish purple.
Fruit: Capsule few, very hard and woody, 4-angled, tapering to a short sterile beak, with a prominent median ridge on each valve, tardily dehiscent for ca. 1/3 the capsule length.
Seeds: Seeds 30-60, in 1 or 2 overlapping rows in each locule, asymmetrically cuneiform to rhombic, irregularly angled, sometimes with a small wing at the distal end or a raised ridge along a longitudinal margin, the surface beaded.
Chromosomes: Chromosome numbers: n = 7, 14; x = 7.