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Key to Oenothera

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1 Flowers zygomorphic (except O. curtiflora and O. glaucifolia), white to pink; petals distinctly clawed, blades elliptic to narrowly obovate, rounded at apex; fruits indehiscent; seeds 1-6 (-8) per capsule, 1.5-3.5 mm long; [section Gaura]
1 Flowers actinomorphic, yellow or white to pink; petals not notably clawed, elliptic to broadly obcordate; fruit dehiscent; seeds (10-) 50-many per capsule, 0.3-2 mm long.
  2 Capsules lanceoloid to cylindric (roughly isodiametric or thickest below middle), nearly terete except for shallow grooves along valves, often curved or contorted; ovary essentially terete (note: buds may be 4-angled).
    3 Flowers white, fading pink; buds nodding; stems white or pink; [western species; in our area only in OK, TX, or as rare waifs eastward].
      4 Seeds in 2 rows per locule, ellipsoid to subglobose, surface with regular longitudinal lines of pits; stems 0.5-3 dm tall or long, decumbent, from large, persistent basal rosettes, cauline leaves reduced; [sect. Kleinia]
      4 Seeds in 1 row per locule, obovoid, surface minutely honeycomb-reticulate, but appearing smooth at lower magnifications; stems 1-10 dm tall, erect and branched, rosettes poorly developed or absent at anthesis; [sect. Anogra].
        5 Plants glabrous proximally, sometimes glandular-puberulent or sparsely strigillose in inflorescence; leaves narrowly lanceolate or oblanceolate, 0.3-0.6 (-1) cm wide, usually entire; stems often single, branched above
        5 Plants densely strigillose; leaves oblong-lanceolate or lanceolate, (0.4-) 0.7-1.5 cm wide, sinuate-dentate or denticulate; stems cespitose, several-many, branched from base or unbranched
    3 Flowers bright yellow, rarely fading pinkish; buds erect; stems green, gray-green, brown, or sometimes flushed red; [collectively widespread].
          6 Stigmas peltate, disc-shaped or shallowly 4-lobed; leaves linear to narrowly lanceolate or oblanceolate, stiff, spinulose-serrate to subentire, less than 1 cm wide; plants perennials less than 6 dm tall, often suffrutescent, stems several to many, branching from near base (O. capillifolia var. capillifolia may be annual and single-stemmed); [MO, s. IL, TX, and OK westward, or disjunct in MS and AL in calcareous soils]; [section Calylophus]
          6 Stigmas deeply divided into 3-4 linear lobes; leaves narrowly to broadly lanceolate to oblanceolate, subentire to deeply sinuate-lobed, up to 6+ cm wide; plants annuals, biennials, or short-lived perennials, stems to 30 dm tall; [collectively widespread]; [section Oenothera]
             7 Capsules lanceoloid, thickest below the middle, tapering to the apex; inflorescence spicate or racemose, dense; plants 3-30 dm tall, erect or ascending
             7 Capsules linear, nearly isodiametric, sometimes very slightly thickened distally; inflorescence lax, appearing to consist of solitary axillary flowers; plants to 4 dm tall, often decumbent; [subsection Raimmania]
               8 Nonflowering portion of stems stiff, densely and uniformly strigillose, sometimes also sparsely villous; leaves thick, gray-green, densely strigillose, subentire, shallowly dentate, or occasionally lyrate; [coastal dunes and barrier islands].
                 9 Sepals 2.0-3.3 cm long; petals 2.5-4.5 cm long; stigma elevated above the anthers at anthesis; capsule 2.5-5.5 cm long; rosette leaves 5-14 cm long, 1-2 cm wide
                 9 Sepals 0.3-1.1 cm long; petals 0.45-1.6 cm long; stigma surrounded by the anthers at anthesis; capsule 1.5-4.5 cm long; rosette leaves 4-8 cm long, 0.7-1.0 cm wide
               8 Nonflowering portion of stem not stiff, sparsely to moderately strigillose, often villous, sometimes densely so; leaves green (sometimes gray-green in O. falfurriae and O. mexicana of inland s. TX), sparsely to moderately strigillose and usually villous, mostly deeply sinuate-lobed or dentate; [sandy soils inland, often disturbed]
                   10 Petals 1.3-4.5cm long, sepals 1-3cm long; styles 3.5-7.5cm long, the stigma lobes slightly to strongly elevated above anthers at anthesis.
                     11 Petals 1.3-2.5cm; styles 3.5-5cm, the stigma lobes only slightly elevated above the anthers at anthesis; [se. TX]
                     11 Petals 2.5-4.5cm; styles 4-7.5cm, the stigma lobes elevated well above the anthers at anthesis; [more widespread]
                   10 Petals 0.5-1.5cm long (sometimes -2.2cm in O. laciniata), sepals 0.5-1.5cm long; styles 2-5 cm long, the stigma lobes surrounded by the anthers at anthesis.
                       12 Bracts flat, spreading, light green; pollen ca. 50% fertile [widespread and weedy]
                       12 Bracts revolute, erect, grayish-green; pollen 85-100% fertile; [se. TX]
  2 Capsules clavate, ellipsoid, or oblong (thickest at or above the middle), strongly 4-8-ribbed or -winged (weakly in O. linifolia); ovary 4-angled or 4-winged.
                          13 Flowers pink or white.
                            14 Petals pink or rose-purple; capsules with rounded ridges, narrowly obovoid, apex narrowed to a sterile beak; [collectively widespread]; [section Hartmannia]
                              15 Flowers rose-purple, petals 4-12 mm long, floral tubes 4-8 mm long; buds erect; capsules narrowed to slender stipe 5-20 mm long; [s. TX]
                              15 Flowers pink, petals 15-45 mm long, floral tubes 12-25 mm long; buds nodding; capsules with thick cylindrical base; [widespread]
                            14 Petals white; capsules with wings 0.5-4mm wide, ellipsoid, broadly rounded to bluntly acuminate; [TX and OK westwards]; [section Leucocoryne]
                                16 Stigmas surrounded by anthers at anthesis; petals 8-25mm; pollen 35-65% fertile
                                16 Stigmas exserted beyond anthers at anthesis; petals 20-43mm; pollen 85-100% fertile
                          13 Flowers yellow, sometimes fading orange or reddish.
                                  17 Leaves all basal, pinnatifid; [section Lavauxia, subsection Lavauxia]
                                  17 Leaves all or partly cauline, entire or toothed.
                                    18 Petals 50-70 mm long; flowers opening in the evening; wings of the fruit 10-25 mm wide; [section Megapterium]
                                       19 Plants strigillose
                                       19 Plants glabrous
                                    18 Petals 3-30 mm long; flowers opening in the day; wings of the fruit <3 mm wide.
                                         20 Cauline leaves linear, < 1 mm wide; petals 3-5 (-7) mm long; floral bracts shorter than the ovaries they subtend; mature fruits ellipsoid-rhomboid, 4-6 mm long, bluntly angled; annual; [section Peniophyllum]
                                         20 Cauline leaves lanceolate to ovate, > 1 mm wide; petals 5-30 mm long; floral bracts longer than the ovaries they subtend; mature fruits clavate to oblong-elliptic, 3.5-20 mm long, mostly narrowly winged; perennial (O. spachiana annual); [section Kneiffia].

Key to Oenothera, Key A: section (or genus) Gaura

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1 Pedicels (0.5-) 1-4 mm long; fruit with a slender stipe (0.5-) 2-10 mm long at maturity; clumped or mat-forming perennials from woody rhizomes or rootstocks; [subsection Stipogaura].
  2 Stems and leaves densely soft-villous, hairs mostly appressed; plants suffrutescent, grayish-green; [c. TX and OK westwards].
    3 Stems strigillose (in addition to the longer villous pubescence); plants often stipitate-glandular
    3 Stems hispidulous (in addition to the longer villous pubescence); stipitate glands absent
  2 Stems and leaves glabrous, strigillose, or spreading-villous; plants not suffrutescent.
      4 Stems conspicuously spreading-villous with hairs 2-4 mm, also ± strigillose; cauline leaves 1-3 (-7) cm long; stems ascending, 3-7 (-12) dm; [s. TX]
      4 Stems glabrous or strigillose, rarely sparsely villous proximally; cauline leaves (1-) 2.5-12 cm long; stems erect, 4-25 (-30) dm.
        5 Plants aggressively rhizomatous (also with a taproot), mat-forming; stems, leaves, and inflorescences glabrous or inconspicuously strigillose
        5 Plants single-stemmed or cespitose, taprooted; plants glabrate to densely strigillose, sometimes also villous or glandular-puberulent.
          6 Stamens presented in lower 1/2 of flower at anthesis; mature capsules narrowly ovoid or lanceoloid; stems sparsely strigillose to glabrate; [gypsum, caliche, and other arid calcareous substrates; c. and w. TX]
          6 Stamens evenly distributed at anthesis; mature capsules ovoid; stems sparsely to densely strigillose [various habitats; LA eastward]
1 Pedicels 0-1 mm long; fruit sessile or with thick cylindric base 0.2-2.2 mm long; annuals or biennials (O. hispida, O. suffrutescens, and O. lindheimeri perennial).
             7 Flowers small, with sepals 2-3.5 mm long, petals 1.5-3 mm long; anthers ellipsoid, ca. 1 mm long; inflorescences long, densely spicate, flexuous and conspicuously nodding apically (stiffening in fruit); [subsection Schizocarya]
             7 Flowers larger, with sepals 2.5-12 mm long, petals 2.5-15 mm long; anthers linear, 1.5-6 mm long; inflorescences erect, not as above.
               8 Flowers essentially actinomorphic, the petals abruptly clawed, blades broadly rhombic-ovate, bright white; fruits 3-4 mm long; leaves narrowly oblong-lanceolate, auriculate at base, entire; inflorescences densely spicate, long and wandlike, stiff; [section Stenosiphon]
               8 Flowers zygomorphic, petals more gradually narrowed to clawed base, white or pinkish; fruits 4-13 mm long; leaves mostly broader or toothed; inflorescences mostly shorter, looser.
                 9 Fruit pyramidal, abruptly constricted below to cylindric base about 1/2 the length and 1/4-1/2 the width of the body; plants perennial, with creeping rhizomes or with woody caudices; [west of the Mississippi River].
                   10 Fruits 7-13 mm long, 3-5mm wide, glabrous or nearly so, base of pyramidal portion bulging; inflorescences loose; leaves usually sinuate-lobed, green; pubescence of stems and leaves relatively sparse, stiffly erect or incurved; plants rhizomatous, stems irregularly branched or single; [subsection Xenogaura]
                   10 Fruits 4-9 mm long, 1-3 mm wide, densely strigillose, base of pyramidal portion not bulging; leaves entire or remotely serrate, bluish-green; pubescence of stems and leaves very dense, whitish, appressed; plants from woody caudices, branched belowground or near soil surface; [subsection Campogaura]
                 9 Fruit fusiform to ellipsoid, ovoid, or obovoid, not abruptly constricted; plants annuals or biennials, rarely monocarpic perennials (except O. lindheimeri); [collectively widespread].
                     11 Plants perennial, branched from base; sepals spreading-villous, stems spreading-villous at least proximally, usually stipitate-glandular in inflorescence, not strigillose; flowers large, opening at sunrise, with petals 10-15 mm long, rhombic-obovate or broadly elliptic, sepals 9-17 mm long; [native in coastal prairies of sw. LA and e. TX, widely cultivated, sometimes naturalizing]
                     11 Plants annual or biennial (rarely monocarpic perennial); sepals glabrous to strigillose (rarely short hirtellous), stem pubescence various, but often strigillose; flowers opening at sunset (except O. demareei), petals 3.5-15 mm long, often narrower, sepals 2.5-18 mm long.
                       12 Capsules narrowly (3-) 4-winged, furrowed between the wings; stems 1.5-6.5 (-12) dm, spreading-villous proximally, glabrate distally (rarely somewhat strigillose); [west of the Mississippi River, or disjunct in sw. MS]
                          13 Flowers with sepals 10-15 mm long, petals 8-13 mm long; leaf margins subentire to shallowly sinuate-dentate; fruits ovoid, broadest near base
                          13 Flowers with sepals 11-21 mm long, petals 10-15 mm long; leaf margins mostly distinctly sinuate-dentate; fruits ellipsoid, broadest near midlength
                       12 Capsules 3-4-angled; stems 5-40dm (shorter in G. triangulata), villous, hirtellous, glandular-puberulent, and/or strigillose (see below); [collectively widespread].
                            14 Flowers small, often 3-merous or a mixture of 3-4-merous, with sepals 2.5-8 mm long, petals 3.5-8 mm long; fruits 3-4-angled; stems mostly branching from near the base, often from persistent rosettes, the inflorescence of relatively few, narrow, ±spicate branches; [acid sandy soils; TX and OK, or FL and outer coastal plain from NC to se. MS].
                              15 Capsules 3-4-angled, ovoid to ellipsoid, broadest at or below the middle; plants robust, stems 6-18 dm tall; [MS eastwards]
                              15 Capsules usually 3-angled, narrowly obovoid, broadest above the middle; plants short, stems 1.5-6.5 (-8.5) dm tall; [TX and OK]
                            14 Flowers larger, 4-merous, with sepals 5-20 mm long, petals 6-17 mm long; fruits 4-angled; plants usually copiously branched at and above the middle, the inflorescence open and diffuse; [of a variety of substrates, often calcareous; widespread inland]
                                16 Stems and leaves conspicuously spreading-villous at least proximally, lacking strigillose hairs, and also glandular-puberulent in inflorescence (rarely glabrate); pollen 35-65% fertile; [Northeast and Upper Midwest south to n. AL and GA, absent from the Coastal Plain southward]
                                16 Stems and leaves densely and finely appressed-strigillose nearly throughout, sometimes also sparsely villous or short-hirtellous, glandular-puberulent or not in inflorescence; pollen 90-100% fertile; [mostly west of the MS river, eastward to AL, TN, KY].
                                  17 Plants exclusively appressed-strigillose; flowers opening at sunrise; [endemic to w. AR and adjacent se. OK]
                                  17 Plants usually hirtellous or villous on lower stems or leaf midribs, or glandular-puberulent in the inflorescence; flowers opening at sunset; [more widespread]

Key to Oenothera, Key B: section (or genus) Calylophus

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1 Buds terete, the sepals without keeled midribs; stamens subequal; petals acute to obtuse; [sw. NE and c. OK and TX westward]; [subsection Salpingia]
  2 Flowers opening in morning; floral tubes 5-25 (-33) mm long, the upper half or more funnelform; plants glandular-puberulent.
  2 Flowers opening in late afternoon or evening; floral tubes 15-60 (-70) mm long, the upper half or less funnelform; plants glabrous, strigillose, hirtellous, or pilose, sometimes also with glandular pubescence in inflorescence; [Oenothera hartwegii complex]
    3 Leaf base clasping, truncate or subcordate; plants densely pubescent with a mixture of hairs, short-pilose and often hirtellous, sometimes also strigillose and glandular-puberulent in the inflorescence
    3 Leaf base attenuate to obtuse; plants glabrous or sparsely strigillose, sometimes glandular-puberulent in inflorescence.
      4 Plants glabrous throughout, or sometimes glandular-puberulent in inflorescence; blades linear to oblanceolate or lanceolate, margins entire to subentire, rarely undulate
      4 Plants sparsely strigillose, sometimes also glandular-puberulent in inflorescence; blades mostly oblanceolate or lanceolate, margins serrulate to subentire, undulate
1 Buds 4-angled, sepals with conspicuously keeled midribs; stamens of 2 lengths, antisepalous filaments about 2× as long as antipetalous filaments; petals truncate to emarginate; [more widespread]; [subsection Calylophus].
        5 Stigmas surrounded by anthers; petals 5-12 (-20) mm long; pollen 30-60 (-80)% fertile.
          6 Pubescence densely and finely strigillose; leaves linear to narrowly lanceolate or oblanceolate, 1-9 cm long, margins subentire to spinulose-serrate (if coarsely spinulose-serrate, longer than 3.5 cm); [widespread in the Great Plains]
          6 Pubescence rather sparse, hairs stout; leaves mostly oblanceolate, 1.5-3.5cm long, margins coarsely spinulose-serrate; [dunes, sandy soil; endemic to se. TX, mostly along the coast]
        5 Stigmas exserted beyond anthers; petals (6-) 9-25 mm long; pollen 90-100% fertile.
             7 Plants perennial from a woody rootstock, stems several to many, erect to decumbent, 1-4 dm tall or long; leaves 1-4 cm long; [TX westward]
             7 Plants annuals or short-lived perennials, stems one to several, erect, 3-8 dm tall; leaves 2.5-9 cm long; [disjunct eastward as far as AL in calcareous substrates].

Key to Oenothera, Key C: section Oenothera, subsections Oenothera and Candela

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1 Petals rhombic-ovate to elliptic, widest near midlength, acute to broadly rounded; seeds ellipsoid, regularly pitted, borne ascending in locules; leaf margins deeply sinuate-lobed to subentire; [subsection Candela].
  2 Petals 5-17 mm long; stigmas surrounded by anthers at anthesis; pollen ca. 50% fertile.
    3 Inflorescence dense, with > 2 flowers per spike opening each day; leaves gray-green; [midwestern, south to KY and AR, or as a waif southwards and eastwards]
    3 Inflorescence lax, 1-2 flowers per spike opening on each day; leaves green; [southeastern Coastal Plain]
  2 Petals 15-35mm; stigmas exserted well beyond anthers at anthesis; pollen 85-100% fertile.
      4 Pedicels, sepals, and capsules densely to sparsely appressed-strigillose, sometimes also with a few stipitate glands; mature flower buds not overtopping spike apex; free sepal tips 0.5-1.5 mm long; petals mostly bluntly acute to short-acuminate; [primarily of the Great Plains and Midwest, southwest to AK, IL, e. TX, and nw. LA]
      4 Pedicels, sepals, and capsules usually glandular-puberulent, spreading-villous, hirsute with pustulate-based hairs, or glabrate; mature flower buds overtopping spike apex; free sepal tips 1-6 mm long; petals mostly broadly rounded; [primarily southeastern, e. TX north to AK and east to AL].
        5 Inflorescences loose, unbranched; bracts 0.5-1.7 cm long, shorter than capsules; capsules hispid with pustular-based hairs; flower buds with free sepal tips 1-3 mm long, glandular-puberulent but not hispid; [endemic to se. TX]
        5 Inflorescences dense, often branched; bracts 1-3 cm long, longer than capsules; [more widespread].
          6 Flower buds with free sepal tips 2-6 mm long, divergent; flower buds, ovaries, or capsules at least sparsely hirsute with spreading, pustulate-based hairs, often also glandular-puberulent; [e. TX east to LA and sw. AK, introduced in MO]
          6 Flower buds with free sepal tips 1-3 mm long, erect; flower buds, ovaries, and capsules glabrate or glandular-puberulent; [endemic to AL and MS]
1 Petals obcordate, widest near the apex, deeply to shallowly emarginate (rarely truncate); seeds prismatic and angled, irregularly pitted, borne horizontally in locules; leaf margins remotely dentate to subentire, or weakly sinuate-dentate near base; [subsection Oenothera].
             7 Stigma well-elevated above the anthers at anthesis; petals (2.5-) 3-5 cm long; anthers 8-22 mm long; pollen 90-100% fertile (except O. glazioviana).
               8 Cauline leaves 0.4-1.0 cm wide; apex of the inflorescence curved; free sepal tips subterminal, divergent; capsules spreading at nearly right angles to the stem, conspicuously curved upward, long-attenuate
               8 Cauline leaves 1.5-6 cm wide; apex of the inflorescence erect; free sepal tips terminal, erect; capsules erect or slightly spreading.
                 9 Floral tubes (6-) 8-12 cm long, styles 9-17 (-20) cm long, buds 7-12 mm in diameter; capsules 6-12 mm in diameter; plants predominately densely appressed-strigillose (sometimes also glandular-puberulent in the inflorescence and sparsely appressed-villous), lacking or rarely with a few pustulate-based hairs; [TX, OK, and NE]
                 9 Floral tubes (2-) 3-4.5 (-5) cm long, styles 5-9 cm long, buds 5-10 mm in diameter; capsules 3.5-7 mm in diameter; plants usually with spreading, pustulate-based hairs in addition to the strigillose pubescence, or appearing nearly glabrous to the unaided eye.
                   10 Upper stems, ovaries, and floral tubes often appearing glabrous to unaided eye, sometimes glandular-puberulent, rarely somewhat strigillose; pustulate-based hairs absent or scattered and translucent; sepals yellow-green
                   10 Upper stems, ovaries, and floral tubes conspicuously strigillose and villous, also sometimes glandular-puberulent; pustulate-based hairs reddish-based (when fresh), often abundant; sepals often reddish-striped or flushed with red
                     11 Cauline leaves 2.5-4 cm wide, bright to dark green, usually with strongly crinkled margins; pollen ca. 50% fertile; ca. 50% of seeds abortive; [exotic; uncommonly cultivated, rarely naturalizing]
                     11 Cauline leaves 1-2.5 cm wide, dull green or gray-green, not crinkled; pollen 90-100% fertile; few seeds abortive; [native; TX and OK westward]
             7 Stigma surrounded by or below the anthers at anthesis; petals 0.7-2.5(-3) cm long; anthers 3-10 mm long; pollen ca. 50% fertile.
                       12 Free sepal tips subterminal (or terminal in O. nutans) in bud, 0.5-5 mm long, usually divergent; inflorescences often curved at apex; capsules rusty brown or greenish black when dry; [primarily of the Northeast and Upper Midwest, south to n. GA and nw. SC in the mountains].
                          13 Stems densely silky-strigillose, the hairs appressed, sometimes also with scattered pustular-based hairs distally; leaf blades grayish-green; dry capsules rusty-brown; leaves 0.5-3 cm wide
                          13 Stems often nearly glabrous in inflorescence, predominantly villous and glandular-puberulent, sometimes also sparsely strigillose; leaf blades bright green; dry capsules greenish-black or dull green; leaves (1-) 1.5-7 cm wide.
                            14 Petals 1.4-2.5 (-3) cm, fading pale yellowish-white to translucent; bracts caducous, pale green; free sepal tips terminal in bud; capsules usually dull green when dry
                            14 Petals 0.8-1.5 (-2) cm, fading pale yellow or orange; bracts persistent, green; free sepal tips subterminal in bud; capsules usually greenish-black when dry
                       12 Free sepal tips terminal in bud, 0.5-3mm long, erect or slightly divergent; inflorescences erect at apex; capsules dull greenish or gray-green when dry; [collectively widespread].
                              15 Stems appearing nearly glabrous in inflorescence (sepals, ovaries, and corolla tubes often strigillose and/or glandular-puberulent), strigose and villous below with translucent (at least in fresh material) hairs
                              15 Stems conspicuously and often densely strigillose, villous, and/or glandular-puberulent throughout, hairs with reddish pustular bases often abundant.
                                16 Stems, leaves, ovaries, capsules, and corolla tubes sparsely to moderately strigillose and glandular puberulent, usually also with abundant spreading, pustular-based hairs; leaves green; sepals usually green or yellowish; [mostly east of the Mississippi River]
                                16 Stems, leaves, ovaries, capsules, and corolla tubes densely strigillose, appearing exclusively appressed-pubescent without magnification (also with some appressed or subappressed pustular-based hairs and rarely glandular-puberulent in the inflorescence); leaves grayish-green; sepals usually red-striped or flushed red; [mostly west of the Mississippi River, scattered eastward as an introduction]

Key to Oenothera, Key D: section Kneiffia

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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]