Oenothera sect. Kneiffia
Oenothera fruticosa
narrow-leaf evening-primrose
usually erect or ascending, sometimes decumbent, branched or unbranched.
erect to decumbent, branched or unbranched, (10–)30–80 cm.
in a basal rosette and cauline, cauline 3–10(–13) cm;
blade margins entire, subentire, denticulate, or coarsely dentate.
in a basal rosette and cauline, rosette usually withered by anthesis, surfaces sometimes glaucous, especially abaxially, basal 3–12 × 0.5–3 cm, petiole 1–4 cm, blade oblanceolate to obovate, margins subentire, dentate, or denticulate, sometimes undulate;
cauline 2–6(–11) × (0.1–)0.5–2(–5) cm, petiole 0.1–2(–6) cm, blade linear, lanceolate to oblanceolate, narrowly elliptic, or ovate, margins subentire or dentate or denticulate, sometimes undulate.
solitary flowers in axils of distal leaves.
usually erect, rarely nodding, flowers in axils of distalmost few nodes.
opening near sunrise, faintly scented;
buds erect, terete, with free tips;
floral tube 3–25 mm;
sepals splitting along one suture, remaining coherent and reflexed as a unit at anthesis, or separating in pairs, or all separating individually;
petals yellow, fading pale pink or lavender, or orangish pink or yellow, or not changing color, obcordate to obovate;
stigma deeply divided into 4 linear lobes.
opening near sunrise;
buds with free tips 0.5–8(–13) mm, connivent, sometimes spreading;
floral tube 5–20 mm;
sepals 5–20 mm;
petals pale to bright yellow, fading pale pink, orangish pink, or yellow, (8–)15–25(–30) mm;
filaments 5–15 mm, anthers 4–7 mm, pollen 85–100% fertile;
style 12–20 mm, stigma exserted beyond anthers at anthesis.
leathery, straight, usually clavate or oblong, sometimes ellipsoid, angled or winged, apex rounded to truncate or weakly emarginate, tapering to a sterile, pedicel-like base (stipe), valve midrib raised, initially apically dehiscent, eventually dehiscent nearly throughout;
sessile.
clavate to oblong-clavate or oblong-ellipsoid, 4-angled to 4-winged, (5–)10–17(–20) × (2–)3–4(–6) mm, stipe 0.1–10 mm;
sessile.
usually numerous, clustered in each locule, ovoid, surface minutely papillose.
1 × 0.5 mm.
= 14, 28, 42, 56.
Oenothera sect. Kneiffia
Oenothera fruticosa
Species 6 (6 in the flora).
Section Kneiffia consists of six species (seven taxa) widely distributed in the eastern half of the United States and adjacent Canada, at 0–1900 m elevation (G. B. Straley 1977). Oenothera spachiana is the only annual species and occurs in open fields, prairies, rocky or sandy sites, and along roadsides; the remaining species are all perennial and occupy diverse habitats, including fresh and brackish swampy areas, wood margins, meadows, prairies, and sandy sites. Three species are self-incompatible (O. fruticosa, O. pilosella, and O. riparia) and the other three are self-compatible (O. perennis, O. sessilis, and O. spachiana). The flowers are diurnal, opening near sunrise and closing near sunset; in some populations of outcrossing species they may reopen for several days. In the outcrossing taxa, the flowers are pollinated by bees (Halictidae and Bombus). Oenothera spachiana and O. perennis are autogamous, the former often cleistogamous and the latter a PTH species. Taxonomy of the section here differs somewhat from Straley in that molecular data (K. N. Krakos et al. 2014) indicate that O. sessilis should be recognized at the species level since the closest relative is O. fruticosa, not O. pilosella as previously thought. Similarly, O. riparia is separated from O. fruticosa since it apparently is most closely related to O. perennis despite the morphological resemblance to O. fruticosa.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Subspecies 2 (2 in the flora).
Oenothera fruticosa as delimited here is a polymorphic species. Previous classification of this group has undergone numerous reorganizations due to the difficulties in separating populations into discrete morphological taxa. In the past it has most frequently been treated as two species, O. fruticosa and O. tetragona Roth, often with a dozen or more infraspecific taxa recognized. The broad delimitation of G. B. Straley (1977) is followed here with one species consisting of two subspecies that appear to intergrade extensively across a wide area of overlap. Straley determined O. fruticosa to be self-incompatible and polyploid.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Herbs annual, from a taproot; flowers in leaf axils in distal 1/2 of plant. | O. spachiana |
1. Herbs perennial, from fibrous roots, sometimes producing rhizomes; flowers in axils of distalmost few nodes of plant. | → 2 |
2. Stigmas surrounded by anthers at anthesis; petals 5–10 mm; inflorescences nodding; pollen 40–70% fertile. | O. perennis |
2. Stigmas exserted beyond anthers at anthesis; petals (8–)15–30 mm; inflorescences usually erect, sometimes nodding; pollen 85–100% fertile. | → 3 |
3. Plants usually exclusively hirsute, rarely glabrous, from fibrous roots and producing rhizomes. | O. pilosella |
3. Plants usually strigillose, glandular puberulent, glabrate, or glabrous, sometimes villous, usually with fibrous or fleshy roots, not or rarely producing rhizomes. | → 4 |
4. Capsules ellipsoid, 8–10 mm; plants densely strigillose, glabrate proximally. | O. sessilis |
4. Capsules clavate to oblong-clavate or oblong-ellipsoid, (5–)10–17(–20) mm; plants usually strigillose, and/or glandular puberulent, or glabrous, sometimes villous. | → 5 |
5. Plants usually moderately to densely strigillose throughout, sometimes and/or glandular puberulent or villous; cauline leaf blades 0.1–1(–1.7) cm wide, margins entire or weakly and remotely denticulate. | O. fruticosa |
5. Plants glabrous or sparsely strigillose, sometimes also glandular puberulent distally; cauline leaf blades (0.2–)0.8–3(–5) cm wide, margins dentate to remotely denticulate. | → 6 |
6. Roots fibrous; leaf blade margins dentate to remotely denticulate; petioles 0.1–2(–6) cm; inland upland meadows, stream margins, edges of woods. | O. fruticosa |
6. Roots somewhat fleshy, with adventitious roots where submerged; petioles 0–1.5 cm; leaf blade margins remotely denticulate; coastal marshes, slow-running rivers. | O. riparia |
1. Capsules clavate to oblong-clavate, widest above middle; plants moderately to densely strigillose, and/or sometimes glandular puberulent or villous; leaf blade margins subentire or weakly and remotely denticulate. | subsp. fruticosa |
1. Capsules oblong to oblong-ellipsoid, widest at middle; plants glandular puberulent or glabrous, sometimes villous or strigillose; leaf blade margins dentate to remotely denticulate. | subsp. tetragona |
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