Taxonomic changes in Oenothera sections Gaura and Calylophus (Onagraceae).

The long-recognized genus Gaura was shown recently to be deeply nested within one of two major clades of Oenothera. New molecular data indicate further taxonomic changes are necessary in Oenothera sect. Gaura. We make these changes here, including three new combinations, in advance of the Onagraceae treatment for the Flora of North America. The new phylogenetic studies show that several pairs of taxa treated as subspecies in the most recent revision by Raven and Gregory (1972) had independent origins within sect. Gaura, and are here elevated to species level (Oenothera nealleyi for Gaura suffulta subsp. nealleyi; Oenothera dodgeniana for Gaura neomexicana subsp. neomexicana; and Oenothera podocarpa for Gaura hexandra subsp. gracilis). Also, a nomenclatural problem in Oenothera sect. Calylophus is corrected by adopting the name Oenothera capillifolia Scheele for the species known previously, and nomenclaturally correct, as Calylophus berlandieri Spach. This problem necessitates a new combination Oenothera capillifolia subsp. berlandieri.

sect.

The molecular studies by Hoggard et al. (2004) and Levin et al. (2004) showed that the genus L. is deeply nested within L. Wagner et al. (2007) in an overall revision of the Onagraceae at the generic and sectional level transferred the species of into and made the group one of 18 sections of . sect. (L.) W. L. Wagner & Hoch is subdivided into eight subsections, with subsect. (L.) W. L. Wagner & Hoch, which consists of 10 species (13 taxa) as delimited by Wagner et al. (2007), shown to be monophyletic by Hoggard et al. (2004) and Levin et al. (2004). Subsequent analyses by Krakos (2011; unpubl.; Fig. 1), which sampled all 13 taxa of subsect. , showed that none of the three species (, , and ) subdivided into subspecies by Raven and Gregory (1972) and maintained in by Wagner et al. (2007) were monophyletic. The relevant topologies revealed by Krakos (unpubl.) that indicate separate origins for these taxa are: 1) a strongly supported clade consisting of , W. L. Wagner & Hoch, and (Buckley) W. L. Wagner & Hoch, but excluding , which is in a weakly supported grade sister to the clade; 2) is the first branch of a well-supported clade consisting of (P. H. Raven & D. P. Gregory) W. L. Wagner & Hoch, (Engelmann & A. Gray) W. L. Wagner & Hoch, , W. L. Wagner & Hoch, (Small) W. L. Wagner & Hoch, (Small) W. L. Wagner & Hoch, and , whereas is sister to this clade plus the clade; and 3) and , come out well-supported in different parts of the clade described in #2. These results are consistent with those of Hoggard et al. (2004); however, that study did not include either or . These results are also consistent with those of Levin et al. (2004), which did include , but not .

Figure 1.

Portion of a Bayesian tree of sect. within a larger analysis of one of two major clades of , which has been referred to as clade B by Wagner et al. (2007) with several outgroup species of the other major clade (A) of from Krakos et al. (unpubl.). The phylogeny is based on nuclear sequences of ITS and ETS and the chloroplast markers rps16, ndhF, trnL-F, and rbcl. The labels use the most recent prior taxonomy, placing the group in (Wagner et al. 2007), using the taxon delimitations of Raven and Gregory (1972). The taxa involved in the proposed changes here are in bold. Numbers above nodes indicate Bayesian posterior probability values.

Below we provide the nomenclature, revised descriptions, and geographic and ecological ranges for all six species of subsect. involved in these changes. We also provide a key to all 13 species of subsect. .

(J. M. Coulter) Krakos & W. L. Wagner comb. nov.

urn:lsid:ipni.org:names:77133597-1

http://species-id.net/wiki/Oenothera_nealleyi

Basionym.

J. M. Coulter, Contr. U.S. Natl. Herb. 1: 38. 1890. (J. M. Coulter) P. H. Raven & Gregory, Mem. Torrey Bot. Club 23: 81. 1973 [“1972”]. (Engelmann ex A. Gray) W. L. Wagner & Hoch subsp. nealleyi (J. M. Coulter) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 214. 2007.

Type.

United States. Texas: Presidio County, Chenate [Chinati] region, 1889, G. C. Nealley 545 [the species entry number (150) from Coulter’s publication also on sheet below 545] (Holotype: US-00015158!; isotype: F!).

Engelmann ex A. Gray var. terrellensis Munz, Bull. Torrey Bot. Club 65: 121. 1928.

Type: United States. Texas: Terrell County, Sanderson, 1 May 1934, V. L. Cory 8469 (Holotype: POM-200873; Isotype: TAES).

Annual from a stout taproot, usually branched from the base, 20–70 (-100) cm tall, villous proximally, the leaves subglabrous or sparsely villous along the veins and margins, becoming glandular puberulent in the distal portion of the plant, especially on the outside of the floral tube and the sepals. Leaves: rosette leaves lyrate, 3.5–9 × 0.5–1.5 cm, gradually narrowed to the petiole, cauline leaves 1.5–7 × 0.1–0.6 cm, narrowly lanceolate to linear, margin sinuate-dentate, undulate, subsessile. Flowers 4-merous, opening at sunset; floral tube 10–20 mm; sepals 11–21 mm; petals 10–15 mm; staminal filaments 8–13 mm, anthers 2–6 mm, pollen 90–100% fertile; style 22–36 mm. Capsule indehiscent, 4.5–8 × 2–5 mm, nut-like, hard, woody, not reflexed, the body ellipsoid or ovoid, broadly winged on the angles and deeply furrowed between the angles, lower angles or projections of the wings at or above the middle prominent; stipe 0.2–2.2 mm long. Seeds 3–4 (-5), 2–3 (-4) mm, ovoid, usually flattened on one or several sides by crowding in the fruit, yellowish to light brown. Gametic chromosome number: n = 7. Self-incompatible.

Phenology and distribution.

Flowering from April to October. Trans-Pecos Texas and northern Coahuila, Mexico, north to Bernalillo and Torrance counties, New Mexico, in washes and other sandy places, grasslands, and extending to pinyon-juniper woodlands; 1220–2140 m.

Raven and Gregory (1972) considered PageBreak to represent an unevenly intergrading entity with based on geographical merging of some of the characteristics that distinguish them and because the entity from Terrell County, Texas, described as var. terrellensis Munz has a combination of characteristics of the two taxa. The origin of these plants from Terrell County should be further explored. For now we here continue to include this name in the synonymy of . The molecular data (Krakos 2011; unpubl.) suggest that is not as closely related to as suggested by Raven and Gregory (1972), given the placement in the phylogeny and the difference in scent profiles for these two taxa. is a member of a strongly supported clade (Fig. 1) consisting of it along with and , while is a member of a polytomy that consists of other species of subsect. , with the - - clade sister to it. has a strong sweet scent, characterized by benzaldehyde (almond), cinnamaldehyde, cinnamic alcohol (cinnamon), methyl salicylate and its methyl ether (wintergreen), neral and geranial (citronella), and nerol and geraniol (lemon) (R. Raguso, pers. comm.), whereas does not have a discernible scent. This difference in scent probably plays a key role in the pollination syndromes for these species.

(Engelmann ex A. Gray) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 214. 2007.

http://species-id.net/wiki/Oenothera_suffulta

Engelmann ex A. Gray, Bost. J. Nat. Hist. 6: 190. 1850.

United States. Texas: Comal County, New Braunfels, May 1847, F. Lindheimer 611 (Lectotype, designated by Raven & Gregory, 1972 [1973]: 80, GH- 00054125!; Isolectotypes: BM, F!, GH [3]!, K [2]!, LE, M!, MO [3]!, NY!, PH, TEX!,, US[2]!, YU!).

Annual from a stout taproot, moderately branched from the base, 25–120 cm tall, villous proximally, the leaves subglabrous or sparsely villous along the veins and around the margins, becoming glabrous distally or rarely sparsely villous on the bracts. Leaves: rosette leaves 7–11 × 0.1–2.3 cm, lyrate, gradually narrowed to the petiole; cauline leaves 1–9.5 × 0.1–2.3, narrowly lanceolate to linear, margin sinuate-dentate, undulate, subsessile. Flowers 4-merous, opening at sunset; floral tube 6.5–14 mm; sepals 11–21 mm; petals 10–15 mm; staminal filaments 6–9 mm, anthers 2–6 mm, pollen 90–100% fertile; style 16–32 mm. Capsule indehiscent, 4.5–8 × 2–5 mm, nut-like, hard, woody, not reflexed, the body ellipsoid or ovoid, broadly winged on the angles and deeply furrowed between the angles, without prominent lower corners or projections of the wings at or above the middle; stipe 0–1 mm long. Seeds (1-)2–4, 2–2.5 mm, ovoid, usually flattened on one or several sides by crowding in the fruit, yellowish to light brown. Gametic chromosome number: n = 7. Self-incompatible.

Flowering from April to June. Common in western Texas, but rare elsewhere throughout the state and absent in the Trans-Pecos; southern Oklahoma, east to Tulsa, Okfuskee, and Coal counties, and in Woodward County, in open, sandy places; 10–1010 m.

Krakos & W. L. Wagner nom. nov.

urn:lsid:ipni.org:names:77133475-1

Wooton, Bull. Torrey Bot. Club 25: 307. 1898, non (Small) Munz (1931). (Rydberg) W. L. Wagner & Hoch subsp. neomexicana (Wooton) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 211. 2007.

United States. New Mexico: Lincoln County, White Mts., 6500 ft, 25 Jul 1897, E. O. Wooton 204 (Holotype: US-330429!; Isotypes: AC!, E!, GH!, K!, LE, MIN, MO! ND, NY [2]!, P, US!).

Biennial from a stout fleshy taproot, with a single or a few branches from the base, 50–120 cm tall, villous and strigillose proximally, leaves subglabrous or strigillose, becoming also glandular puberulent distally, and sometimes also sparsely villous. Leaves: rosette leaves 6–20 × 1–3 cm; cauline leaves 5–10 × 1–2.5 cm, lanceolate to narrowly elliptic, subentire to repand-denticulate. Flowers 4-merous, opening at sunset; floral tube 10–11 mm; sepals 11–15 mm; petals 11–13.5 mm; staminal filaments 6.5–9 mm, anthers 2.5–4 mm long, pollen 90–100% fertile; style 22–28 mm. Capsule indehiscent, 9–11 × 3–5 mm, nut-like, hard, woody, not reflexed, the body ellipsoid or ovoid, sharply 4-angled, with fairly deep furrows alternating with the angles for 2–3 mm from the apex, ribbed from base of furrow to base of the fruit. Seeds 2–4, 2–3 mm, yellowish to light brown. Gametic chromosome number: n = 7. Self-compatible.

Flowering from June to September.In the western foothills of the San Juan Mountains in Archuleta County, Colorado, and Rio Arriba PageBreakCounty, New Mexico; Sierra Blanca and Sacramento Mountains in Lincoln and Otero counties, south-central New Mexico. Collected once at Durango, La Plata County, Colorado (Raven and Gregory 1972), but has not since been recollected; found in mountain meadow openings in coniferous forests; 1830–2640 m.

The new name for this species is to honor David and Judy Dodgen of Cloudcroft, New Mexico, landowners who graciously allowed one of us (Krakos) to conduct research on their land, which harbors populations of this rare species. and were considered by Raven and Gregory (1972) to represent a relict species along the eastern flank of the Rocky Mountains that arose from more widespread species farther to the east, such as . The new molecular analyses revealed that is closely related to (Fig. 1). is the first branch of a subclade within the subsect. clade that includes and a terminal sister pair of and . These relationships suggest that may represent a relictual species and have a shared ancestry with . , on the other hand, belongs to a subclade which is sister to that containing , and within that subclade is sister to and . So, although is fairly closely related to , the two taxa seem to have had independent origins that have led to distributions along the eastern flank of the Rocky Mountains.

(Rydberg) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 211. 2007.

http://species-id.net/wiki/Oenothera_coloradensis

Rydberg, Bull. Torrey Bot. Club 31: 572. 1904. var. coloradensis (Rydberg) Munz, Bull. Torrey Bot. Club 65: 114. 1938. (Rydberg) P. H. Raven & Gregory, Mem. Torrey Bot. Club 23: 63. 1973 [“1972”].

United States. Colorado: Larimer County, Ft. Collins, 5000 ft, 8 Jul 1895, J. M. Cowen s.n. (Holotype: NY-BC00232160!; Isotype: GH!).

Biennial from a stout, fleshy taproot, with several branches from the base, 50–80(-100) cm tall, strigillose proximally, becoming glandular puberulent and strigillose distally. Leaves: rosette leaves 4–18 × 1.5–4 cm; cauline leaves 5–13 × 1–4 cm, very narrowly elliptic, subglabrous or strigillose, margin subentire to repand-denticulate. Flowers 4-merous, opening at sunset; floral tube 8–12 mm; sepals 9.5–13 mm; petals 7–12 mm; staminal filaments 6.5–9 mm, anthers 2.5–4 mm, pollen 90–100% fertile; style 19–25 mm. Capsule indehiscent, 6–8.5 × 2–3 mm, nut-like, hard, woody, not reflexed, the body ellipsoid or ovoid, sharply 4-angled, with fairly deep furrows alternating with the angles for 2–3 mm from the apex, ribbed from base of furrow to base of the fruit. Seeds 1–4, 2–3 mm, yellowish to light brown. Gametic chromosome number: n = 7. Probably self-compatible.

Flowering in July and August.In early successional vegetation of the North and South Platte River watersheds on the high plains, sloping floodplains, and drainage base in heavy soils, from southern Laramie and Platte counties in Wyoming, northern Weld County, Colorado, formerly near Fort Collins, Larimer County, Colorado, and in western Kimbal County, Nebraska; 1530–1950 m.

The Colorado butterfly plant is currently known from fewer than two dozen populations and has been federally listed as a Threatened species in the U.S. (USDI Fish and Wildlife Service 2000). The primary threats are agricultural use of habitat, herbicide spraying to control weed species, and livestock trampling and grazing (see Fertig 2000, Heidel and Handley 2011, NatureServe 2013). Recent study by Krakos (unpubl.) has determined this species to probably be self-compatible.

(Wooton & Standley) Krakos & W. L. Wagner comb. nov.

urn:lsid:ipni.org:names:77133476-1

http://species-id.net/wiki/Oenothera_podocarpa

Wooton & Standley, Contr. U.S. Natl. Herb. 16: 154. 1913.

United States. New Mexico: Grant County, Bear Mt., near Silver City, 1500 m, 17 June 1903, O. B. Metcalfe166 (Holotype: US-495277!; Isotypes: DS, E!, G, GH!, LE, MIN!, MO!, NMC! POM, US!).

(Wooton & Standley) W. L. Wagner & Hoch, Syst. Bot. Monogr. 83: 213. 2007.

Wooton & Standley, Contr. U.S. Natl. Herb. 16: 153. 1913. (Wooton & Standley) P. H. Raven & Gregory, Mem. Torrey Bot. Club 23: 87. 1973 [“1972”].

United States. New Mexico: Grant County, Ft. Bayard forest nursery, 29 Aug 1905, J. C. Blumer 44 (Holotype: US-499693!; isotypes: GH!). Epithet not available in as there are two earlier uses: (Phil.) H. Léveillé, 1905 (syn. for Hooker & Arnott) and Schrader ex Fischer & Meyer, 1835 (syn. For L.).

Wooton & Standley, Contr. U.S. Natl. Herb. 16: 154. 1913.

United States. New Mexico: Lincoln County, Wingfields Ranch on Ruidosa Creek, White Mts, 8 July 1895, E. O. Wooton s.n. (Holotype: US-561073!).

Wooton & Standley, Contr. U.S. Natl. Herb. 16: 152. 1913.

United States. New Mexico: Socorro County, Socorro, May 1881, G.R. Vasey s.n. (Holotype: US-45764!).

Wooton & Standley, Contr. U.S. Natl. Herb. 16: 153. 1913.

http://species-id.net/wiki/Gaura_glandulosa

United States. New Mexico: Catron County, Reserve, 9 July 1906, E. O. Wootons.n. (Holotype: US 561072!; Isotype: US!).

Annual herb from a stout taproot, usually well-branched at the base and above, 15–100 cm tall, villous proximally, the leaves subglabrous to densely short-villous, becoming subglabrous, strigillose and/or glandular puberulent distally. Leaves: rosette leaves lyrate, 3–15 × 0.5–1 cm; cauline leaves 1–9 × 0.1–0.8 cm, linear to very narrowly elliptic or narrowly lanceolate, sinuate-dentate to subentire, subsessile. Flowers 4-merous, opening at sunset; floral tube 6–10 mm; sepals 6–12 mm; petals 5.5–9.5 mm; filaments 4–6 mm, anthers 2–3 mm, pollen 90–100% fertile; style 11–18.5 mm. Capsule indehiscent, 6–8 × 2–3 mm, nut-like, hard, woody, not reflexed, broadly winged on the angles and deeply furrowed between the angles, the body ellipsoid or narrowly obovoid, narrowed at the base but not stipitate. Seeds 4, 2–3 mm, ovoid, usually flattened on one or several sides by crowding in the fruit, yellowish to reddish brown. Gametic chromosome number: n = 7. Self-compatible.

Flowering from (May) June to October. In Arizona from eastern Mohave County south through the mountains of central Arizona to eastern Pima County and the southwestern quarter of New Mexico, and in Mexico southward in the Sierra Madre Occidental to eastern Sonora and throughout the western halves of Chihuahua and Durango, often in disturbed sites in or on sandy washes, slopes, grasslands, meadows, pinyon-juniper or ponderosa pine woodlands, and sometimes on volcanic cinders; 760–2750 m.

is the first species to branch off in the subsect. clade (Fig. 1), whereas is nested well within the subsect. clade. The epithet “podocarpa” was selected among the three equally available names at the species rank for this species. Previously, , one of four species published simultaneously by Wooton and Standley,was selected by Munz (1938), while placing the other three into synonymy. Tidestrom and Kittell (1941) apparently unaware of the Munz publication selected , but were incorrect as they should have used . They did not establish any new priority.

(Ortega) W. L. Wagner & Hoch, Syst. Bot Monogr. 83: 212. 2007.

http://species-id.net/wiki/Oenothera_hexandra

Ortega, Hort. matr. dec. 14. 1797.

Based on living plants cultivated at the Royal Botanical Garden in Madrid from seeds sent by Sessé from Mexico [erroneously said to be from Cuba] (Holotype: not located).–Mexico. México. Comunidad Temascaltepec, 19 May 1936, G. B. HinPageBreakton 7688 (Neotype, designated, by Wagner et al. 2007: 212: MO-1717467!; Isoneotypes: C, F, G, GH, LL, MICH, NY, US!).

Annual herb from a stout taproot, usually well-branched at the base and above, 15–100 cm tall, villous proximally, the leaves subglabrous to densely short-villous, and becoming subglabrous, strigillose, and/or glandular-puberulent distally. Leaves in a basal rosette and cauline; rosette leaves lyrate, gradually narrowed to the petiole, usually quickly deciduous; cauline leaves 1–9 × 0.1–0.8 cm, linear to very narrowly elliptic or narrowly lanceolate, margin sinuate-dentate to subentire, subsessile. Inflorescence strict to somewhat branched, 7–53 cm long, bracts 2–5 cm long, narrowly lanceolate to ovate. Flowers 3-merous, opening at sunset; floral tube 4.5–7.5 mm; sepals 3–10 mm; petals 4.5–7 mm; staminal filaments 3–6 mm, anthers 1–2 mm, pollen 90–100% fertile; style 9–14.5 mm. Capsule indehiscent, 4.5–8 × 2–4.5 mm, nut-like, hard, woody, not reflexed, the body ellipsoid or narrowly obovoid, broadly winged on the angles and deeply furrowed between the angles, narrowed at the base but not stipitate. Seeds 3, 1.75–3 mm, ovoid, usually flattened on one or several sides by crowding in the fruit, yellowish to reddish brown. Gametic chromosome number: n = 7. Self-compatible and highly autogamous.

Flowering from March to November. From Durango, Mexico south in the Sierra Madre Occidental to the Trans Mexican Volcanic Belt, where abundant, and in Chiapas, Mexico as well as Guatemala in grasslands, meadows or oak woodlands, or disturbed areas, in sandy soils; 1800–2430 m.

A nomenclatural problem in sect. is corrected here by adopting the name Scheele for the species known previously, and nomenclaturally correct, as Spach when the genus is recognized as distinct from ; however, when this species is considered to be a member of as it was recently by Wagner et al. (2007) based on molecular data (Levin et al. 2004), (Spach) Steudel is not available since it is a later homonym. This problem necessitates a new combination .

Scheele, Linnaea 21: 576. 1848.

http://species-id.net/wiki/Oenothera_capillifolia

(Scheele) Small, Fl. S.E. U.S. 846, 1335. 1903.

United States. Texas: Comal County, NewBraunfels, April (1846?), Ferdinand Roemers.n. (not located). —United States. Texas: Comal County, NewBraunfels, May 1850, F. Lindheimer 809 (Neotype: here designated, US-502186!; Isoneotypes: ARIZ, DS, F, GH, MO!, NMC, NY, OKL, PH, TEX, UC).

Towner (1977) subdivided into two subspecies. We here continue to use his classification with the new nomenclature.

Oenothera berlandieri subsp.

var. pinifolia Engelmann in A. Gray, Bost. J. Nat. Hist. 6: 189. 1850. var. pinifolia (Engelmann) Small, Bull. Torrey Bot. Club 23: 187. 1896. (Engelmann) Munz, N. Amer. Fl., ser. 2, 5: 141. 1965. (Engelmann) Towner, Ann. Missouri Bot. Gard. 64: 107. 1977.

United States. Texas: Comal County, New Braunfels, Apr-May 1846, F. Lindheimer 394 (Holotype: MO-122323!; Isotypes: DS, GH [2]!, K [3]! MO!, NY!, PH, RSA, US!, YU!).

(Spach) W.L. Wagner & Hoch comb. nov.

urn:lsid:ipni.org:names:77133601-1

Spach, Ann. Sci. Nat. Bot., sér. 2, 4: 272. Nov. 1835. (Spach) Steud., Nom. Bot., ed. 2. 2: 206. 1841, non D. Dietr. Dec. 1840. (Spach) Walp., Repert. Bot. Syst. 2: 79. 1843. Spach subsp. berlandieri (Spach) Towner & Raven, Madroño 20: 243. 1970.

United States. Texas: Bahia del Espiritu Santo [probably in present Calhoun County, March or May 1829], Jean Louis Berlandier 539=1919 (Holotype: P; Isotypes: GH!, PH).

1a	Flowers 3-merous; fruits 3-angled	2
1b	Flowers 4-merous; fruits 4-angled	5
2a	Plants usually unbranched proximally, 60–180 cm tall; fruit narrowly ellipsoid or ellipsoid; coastal plain from Florida to North Carolina	Oenothera simulans
2b	Plants usually branched proximally, 15–65 cm tall; fruits ellipsoid or ovoid	3
3a	Sepals strigillose to subglabrous; pollen ca. 50 % fertile; north-central Texas and Oklahoma	Oenothera triangulata
3b	Sepals strigillose to glandular puberulent; pollen 90–100 % fertile	4
4a	Sepals 3–10 mm; inflorescence usually glandular puberulent; Mexico and Guatemala	Oenothera hexandra
4b	Sepals 10–15 mm; inflorescence strigillose; Texas, Oklahoma, Louisiana, and Alabama	Oenothera patriciae
5a	Flowers opening near sunrise; plants clumped perennial, usually branching from the base, villous throughout and usually glandular puberulent in the distal parts; southeast Texas and Louisiana	Oenothera lindheimeri
5b	Flowers opening near sunset or rarely sunrise (Oenothera demareei); plants annual or biennial, branched or unbranched; villous, strigillose or short-hirtellous throughout, distal parts usually glandular puberulent, short-hirtellous, strigillose, or subglabrous, occasionally villous	6
6a	Fruits angled but not winged; plants (5–)100–400 cm tall	7
6b	Fruits broadly winged on the angles and deeply furrowed between the angles; plants rarely more than 15–100(–120) cm tall	12
7a	Sepals 2.5–8 mm; stem usually single, branched or unbranched from base upwards; coastal plain from Florida to North Carolina	Oenothera simulans
7b	Sepals (7–)9–20 mm; stems usually several, branched from base upwards	8
8a	Flowers opening near sunrise; plants exclusively strigillose throughout; southwestern Arkansas, and perhaps adjacent Texas and Oklahoma	Oenothera demareei
8b	Flowers opening near sunset; plants with some combination of villous, glandular puberulent, short-hirtellous, strigillose, or subglabrous; rarely exclusively strigillose	9
9a	Anthers with pollen 35–65% fertile (sterile pollen smaller); plants villous and glandular puberulent, never strigillose; north-central to north-eastern U.S.	Oenothera gaura
9b	Anthers with pollen 90–100% fertile; plants strigillose, villous, short-hirtellous, or subglabrous	10
10a	Plants annual; fruit 4.5–7 mm; central U.S.	Oenothera filiformis
10b	Plants biennial; fruit 6–11 mm; Colorado, Nebraska, New Mexico, and Wyoming	11
11a	Plants strigillose proximally, becoming glandular puberulent and strigillose distally; Colorado, Nebraska, and Wyoming	Oenothera coloradensis
11b	Plants villous and strigillose proximally, becoming also glandular puberulent distally and only sparsely villous; Colorado and New Mexico	Oenothera dodgeniana
12a	Sepals 11–20 mm; floral tube 7–20 mm	13
12b	Sepals 6–15 mm; floral tube 6–12 mm	14
13a	Plants glabrous distally, except sometimes bracts sparsely villous; fruit sessile	Oenothera suffulta
13b	Plants glandular puberulent distally; fruit on a stipe 0.2–2 mm	Oenothera nealleyi
14a	Sepals 6–12 mm long, glandular puberulent, subglabrous or strigillose; Mexico to Arizona, and New Mexico	Oenothera podocarpa
14b	Sepals 10–15 mm, glabrous or strigillose; Texas, Oklahoma, Louisiana, and Alabama	Oenothera patriciae