1 Plants taprooted annuals, 1-3 dm tall; leaves linear-spatulate or linear-oblanceolate, erect-ascending; flowers borne in leaf axils throughout upper 1/2 of plant

1 Plants fibrous-rooted or rhizomatous perennials, 1-12 dm tall; leaves broader; flowers borne only in uppermost few nodes of branches.

  2 Stems, leaves, and free sepal tips (but often not sepal bodies) coarsely pilose-hirsute with spreading, whitish hairs 1-3 mm long; free sepal tips 1-4 mm long, widely divergent; leaf blades mostly elliptic or elliptic-lanceolate, rugose

  2 Plants sparsely to densely strigillose, glandular, pilose, and/or villous pubescence, not pilose-hirsute (hairs mostly shorter or appressed); sepal tips various; leaf blades various.

    3 Plants exclusively eglandular-pubescent, finely appressed-strigillose on leaves, upper stems, ovaries, and sepals; capsules ellipsoid, broadest at middle, 8-10 mm long, nearly sessile, with stipitate bases 0-2 mm long; [wet prairies and ditches; AR, LA, and e. TX]

    3 Plants usually glandular-pubescent at least on sepals and floral tubes (except O. unguiculata and some forms of O. fruticosa), otherwise variously eglandular-pubescent to glabrous; capsules clavate with elongate stipitate bases, or, if oblong-ellipsoid and nearly sessile, then mostly 10-17 mm long.

      4 Stigmas surrounded by anthers at anthesis; petals 5-10 mm; flowers spaced out along an elongate inflorescence axis, axis nodding distally in bud; capsules narrowly obovoid, glandular-pubescent initially, often glabrate at maturity

      4 Stigmas elevated above anthers at anthesis; petals (8-) 12-35 mm long; inflorescences erect, mostly more compact; capsules various; [Oenothera fruticosa complex].

        5 Leaves 1-4 cm wide, lanceolate to ovate, margins dentate to remotely denticulate; petals (20-) 25-35 mm long; ovaries and capsules moderately glandular-puberulent to glabrous, oblong or oblong-ellipsoid; vegetative parts mostly inconspicuously pubescent (sometimes villous proximally, or sparsely strigillose distally).

          6 Roots fleshy, plants producing adventitious roots where submerged; capsules obovoid, widest near the tip, 15-20 mm long, narrowed to an elongate stipitate base; [coastal rivers and marshes on the outer Atlantic Coastal Plain from VA to SC]

          6 Roots fibrous; capsules oblong or oblong-ellipsoid, widest near the middle, 10-17 mm long, abruptly contracted at the base, often subsessile; [inland, mostly absent from the outer Coastal Plain]

             7 Plants conspicuously bluish-glaucous on leaves, ovaries, pedicels, and often sepals, floral tubes, and upper stems; plants glabrous or nearly so; leaves broadly ovate-elliptic, regularly dentate, often slightly fleshy; [TN, KY, and n. GA, west of the Blue Ridge]

             7 Plants green, or leaves pale abaxially; plants sparsely to moderately pubescent at least in inflorescence or on lower stems; leaves lanceolate to linear-lanceolate, remotely denticulate or sinuate-dentate to subentire, thin-textured or chartaceous.

               8 Leaves 1-3 cm wide, lanceolate, acuminate, thin-textured and lax, margins mostly shallowly sinuate-dentate; petals 25-30mm; plants usually inconspicuously pubescent, sometimes sparsely to moderately spreading-villous on lower stems and leaf veins and glandular-puberulent in the inflorescence, rarely somewhat strigillose on distal leaves and stems; [of moderate to high elevations in the southern Blue Ridge]

               8 Leaves mostly 0.5-1.5 cm wide, narrowly lanceolate, margins variable; petals 12-20mm, rarely longer; stems and leaves usually moderately to densely strigillose to strigose-hirsute, sometimes also glandular-puberulent in the inflorescence; [Northeast and Upper Midwest rarely south to e. KY and c. VA]

        5 Leaves 0.5-1.0 (1.2) cm wide, various, entire or remotely denticulate; petals (8-) 12-20 (-25) mm long; ovaries and capsules densely to sparsely pubescent, hairs eglandular or a mixture of glandular and eglandular (sometimes glabrate at maturity), clavate; vegetative parts densely strigose, strigillose, or pilose.

                 9 Capsules oblong or oblong-ellipsoid, widest near the middle, usually abruptly contracted to a stipitate base 0.1-3 (-7) mm long; ovary and capsule vestiture usually exclusively glandular, rarely with a few eglandular hairs; leaves mostly lanceolate or narrowly lanceolate, widest below the middle; [VA and e. KY northward]

                 9 Capsules clavate (ellipsoid in O. species 2), widest near the tip, gradually tapered to a slender stipitate base 3-15 mm long; ovary and capsule densely to sparsely strigillose, strigose, hirtellous, or pilose, sometimes mixed with glandular hairs.

                   10 Leaves and stems densely velutinous (long, soft hairs); cauline leaves mostly 2-4× as long as wide, lance-oblong or lanceolate, remotely denticulate.

                     11 Ovaries, capsules, floral tubes, and sepals densely short-pilose, hairs predominantly eglandular; [of serpentine barrens in PA and MD]

                     11 Ovaries, capsules, floral tubes, and sepals predominantly glandular-puberulent; [of the Cumberland Plateau of TN, KY, and AL]

                   10 Leaves finely strigose or strigillose, hairs closely appressed, stems strigillose to pilose; leaves linear-oblanceolate, linear-lanceolate, oblanceolate, elliptic, or lanceolate, mostly 5-10× as long as wide, nearly entire (remotely denticulate in O. riparia and O. unguiculata).

                       12 Free sepal tips (1-) 1.5-2.5 (-3) mm long, cartilaginously thickened, divergent; sepals finely strigose, hairs all eglandular and tightly appressed; leaves linear-lanceolate or linear-oblanceolate, often remotely toothed; [tidal marshes, coastal rivers, wet maritime grasslands, and wet pine savannas; outer Atlantic Coastal Plain from SC north to Long Island]

                          13 Plants 7-12 dm tall; vegetative parts inconspicuously strigillose; capsules 15-20 mm long

                          13 Plants 1-8 dm tall; vegetative parts densely appressed-strigose; capsules 6-11 mm long

                       12 Free sepal tips 0-1 (-2) mm long, mostly connivent; sepals glandular-puberulent, pilose, or strigillose; sepals and capsules often with spreading and/or glandular hairs; leaves mostly narrow-elliptic or oblanceolate, essentially entire; [inland, mostly dry or rocky soils; widespread in our region]

                            14 Capsule body 3-5 mm long, subglobose; capsules and ovaries strigose-pilose or strigillose; [of the Piedmont or outer Atlantic Coastal Plain].

                              15 Capsule body 3.5-4 mm long, strigose-pilose; [of Coastal Plain bogs]

                              15 Capsule body 4-5 mm long, very finely strigillose; plants colonial, stoloniferous; [of Piedmont rock outcrops]

                            14 Capsule body 6-11 mm long, obovoid; capsules and ovaries short-pilose, strigillose, hirtellous, and/or glandular-puberulent; [widespread in the southeast]

                                16 Ovaries, floral tubes, sepals, and capsules with loosely ascending, coarse, ±dense pilose pubescence about 1 mm long, glandular hairs lacking or very sparse; [of the Ouachitas and Ozark Plateau of AR and OK]

                                16 Ovaries, floral tubes, sepals, and capsules with eglandular hairs < 1 mm, spreading to appressed, and often mixed with glandular hairs; [widespread east of the Mississippi River]

                                  17 Ovaries, developing capsules, and floral tubes with hairs predominantly glandular, capsules often glabrate at maturity; [SC west to MS and north to s. IL, IN, and OH, west and south of the Blue Ridge]

                                  17 Ovaries, capsules, and floral tubes densely hirtellous or short-pilose, hairs predominantly eglandular; [SC north to PA, east of the Blue Ridge]